2019 Vol. 44, No. 6
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2019, 44(6): 1773-1783.
doi: 10.3799/dqkx.2019.015
Abstract:
To understand the crust-mantle electrical structure and the tectonic feature of Bangong-Nujiang suture, and offer the electrical constraints to its subduction polarity, the magnetotellurics data of the Shenzha-Shuanghu magnetotelluric profile in the central Himalaya-Tibetan Plateau was carefully processed and analyzed, obtaining a reliable 2-D electrical model. The study represents that there are some different scale resistors distributed along the profile in the upper crust and the bottom depth varying from 10 to 25 km, and meanwhile there is a middle-lower conductive layer composed of some discontinuous conductivities beneath the resistive layer. With the analysis of the electric structure, the study indicates that the subduction polarity of the Bangong-Nujiang Tethyan ocean may be double-sided, and subsequently the detachment of the upper crustal resistor was occurred, and so the twice dynamics above may contribute to the formation of the conductor within the suture. Furthermore, the conductor beneath the northern Lhasa terrane may also reflect the relation among the dynamics, magmatism and mineralization.
To understand the crust-mantle electrical structure and the tectonic feature of Bangong-Nujiang suture, and offer the electrical constraints to its subduction polarity, the magnetotellurics data of the Shenzha-Shuanghu magnetotelluric profile in the central Himalaya-Tibetan Plateau was carefully processed and analyzed, obtaining a reliable 2-D electrical model. The study represents that there are some different scale resistors distributed along the profile in the upper crust and the bottom depth varying from 10 to 25 km, and meanwhile there is a middle-lower conductive layer composed of some discontinuous conductivities beneath the resistive layer. With the analysis of the electric structure, the study indicates that the subduction polarity of the Bangong-Nujiang Tethyan ocean may be double-sided, and subsequently the detachment of the upper crustal resistor was occurred, and so the twice dynamics above may contribute to the formation of the conductor within the suture. Furthermore, the conductor beneath the northern Lhasa terrane may also reflect the relation among the dynamics, magmatism and mineralization.
2019, 44(6): 1784-1796.
doi: 10.3799/dqkx.2018.355
Abstract:
In order to investigate the distribution characteristics of the low velocity layer in the central Qiangtang basin, this study conducted the TITAN-Ⅰ teleseismic receiver functions across the Qiangtang basin. And the signal-to-noise ratio of the receiver function was improved by the phase filtering technique in the time frequency domain. Finally, the one-dimensional S wave velocity structure in the depth of 100 km below each station is obtained by the nonlinear inversion of conjugate gradients algorithm for the complex spectrum ratios of receiver function. The results show that the phase filtering method in the time frequency domain can significantly improve the signal-to-noise ratio and make the one-dimensional S wave velocity structure of the subsequent inversion more reliable. The Moho depth of the Qiangtang basin is 58 ±6 km, and where has a higher Poisson's ratio. The low velocity layer in the mid-lower crust is widely distributed. The transverse discontinuity is discontinuous, and the depth is between 20 and 30 km, the thickness of the layer is 6-12 km, the shear wave velocity is 3.4±0.1 km/s. In some areas, there is a thin layer of 4 km thin layer in the mid-upper crust with a depth of 10 km. The low velocity layer in the mid-lower crust of the Qiangtang basin is caused by the deep mantle derived magma upwelling along the tectonic weak zone, resulting in partial melting in the mid-lower crust and upper mantle.
In order to investigate the distribution characteristics of the low velocity layer in the central Qiangtang basin, this study conducted the TITAN-Ⅰ teleseismic receiver functions across the Qiangtang basin. And the signal-to-noise ratio of the receiver function was improved by the phase filtering technique in the time frequency domain. Finally, the one-dimensional S wave velocity structure in the depth of 100 km below each station is obtained by the nonlinear inversion of conjugate gradients algorithm for the complex spectrum ratios of receiver function. The results show that the phase filtering method in the time frequency domain can significantly improve the signal-to-noise ratio and make the one-dimensional S wave velocity structure of the subsequent inversion more reliable. The Moho depth of the Qiangtang basin is 58 ±6 km, and where has a higher Poisson's ratio. The low velocity layer in the mid-lower crust is widely distributed. The transverse discontinuity is discontinuous, and the depth is between 20 and 30 km, the thickness of the layer is 6-12 km, the shear wave velocity is 3.4±0.1 km/s. In some areas, there is a thin layer of 4 km thin layer in the mid-upper crust with a depth of 10 km. The low velocity layer in the mid-lower crust of the Qiangtang basin is caused by the deep mantle derived magma upwelling along the tectonic weak zone, resulting in partial melting in the mid-lower crust and upper mantle.
2019, 44(6): 1797-1808.
doi: 10.3799/dqkx.2018.399
Abstract:
Crustal structure is one of the main targets of deep geophysical exploration in the Qinghai-Tibet Plateau. In this paper, the bi-dimensional empirical mode decomposition (BEMD) separation method combined with power spectrum analysis is studied, and it is applied to the separation of gravity and magnetic anomalies in the Gangdise belt. The model test results show that the method can separate the superimposed anomalies and obtain a reliable estimation of the source depth. The decomposition results in the study area show that the bouguer and the RTP magnetic anomalies can be divided into three anomalies which are induced by three equivalent layer sources from shallow to deep. The deep gravity and magnetic fields are characterized by the north-south partition and the east-west block. It is proved that the Qinghai-Tibet Plateau is formed by splicing the terrains along the north-south direction and after its formation, it is continuously pushed northward by the Indian plate unevenly, which makes the material properties of the Himalayan terrain and the Gangdise terrain have significant differences in deep from east to west bounded by 88°E and 93°-95°E. It is inferred that the low density body is discontinuous in east-west direction and the low density body in the middle and east of the study area is cut by the Yarlung Zangbo suture zone.
Crustal structure is one of the main targets of deep geophysical exploration in the Qinghai-Tibet Plateau. In this paper, the bi-dimensional empirical mode decomposition (BEMD) separation method combined with power spectrum analysis is studied, and it is applied to the separation of gravity and magnetic anomalies in the Gangdise belt. The model test results show that the method can separate the superimposed anomalies and obtain a reliable estimation of the source depth. The decomposition results in the study area show that the bouguer and the RTP magnetic anomalies can be divided into three anomalies which are induced by three equivalent layer sources from shallow to deep. The deep gravity and magnetic fields are characterized by the north-south partition and the east-west block. It is proved that the Qinghai-Tibet Plateau is formed by splicing the terrains along the north-south direction and after its formation, it is continuously pushed northward by the Indian plate unevenly, which makes the material properties of the Himalayan terrain and the Gangdise terrain have significant differences in deep from east to west bounded by 88°E and 93°-95°E. It is inferred that the low density body is discontinuous in east-west direction and the low density body in the middle and east of the study area is cut by the Yarlung Zangbo suture zone.
2019, 44(6): 1809-1821.
doi: 10.3799/dqkx.2019.050
Abstract:
The structure and composition of orogenic belts are important for understanding the chemical evolution of the continental crust and the background for metallogenesis. This study integrates previously published crustal seismic structures, experimentally determined petrophysical properties of various rock types, and geochemical data of magmatic rocks from the southeastern Lhasa Terrane, in order to discuss the compositional features of the continental crust in this region and their possible causes. The average crustal seismic velocity in this region is lower than the average values of global continental crust and orogenic belts, suggesting a more felsic composition for the bulk continental crust. Moreover, the lower crust could also be composed of intermediate rocks (restitic intermediate garnet granulite). The felsic bulk crustal composition of the southeastern Lhasa terrane is supposed to be related to multiple episodes of felsification, including the pre-collisional continental arc evolution stage (mainly by delamination of cumulate or restitic lower crust) and the post-collisional plateau collapsing stage (mainly by delamination of thickened lower crust, which is accompanied by the relamination/tectonic underthrusting of felsic materials from the ancient Indian continental crust). The Lhasa terrane is one of the best places to study the chemical differentiation of continental crust, which demands further comprehensive studies of multiple disciplines.
The structure and composition of orogenic belts are important for understanding the chemical evolution of the continental crust and the background for metallogenesis. This study integrates previously published crustal seismic structures, experimentally determined petrophysical properties of various rock types, and geochemical data of magmatic rocks from the southeastern Lhasa Terrane, in order to discuss the compositional features of the continental crust in this region and their possible causes. The average crustal seismic velocity in this region is lower than the average values of global continental crust and orogenic belts, suggesting a more felsic composition for the bulk continental crust. Moreover, the lower crust could also be composed of intermediate rocks (restitic intermediate garnet granulite). The felsic bulk crustal composition of the southeastern Lhasa terrane is supposed to be related to multiple episodes of felsification, including the pre-collisional continental arc evolution stage (mainly by delamination of cumulate or restitic lower crust) and the post-collisional plateau collapsing stage (mainly by delamination of thickened lower crust, which is accompanied by the relamination/tectonic underthrusting of felsic materials from the ancient Indian continental crust). The Lhasa terrane is one of the best places to study the chemical differentiation of continental crust, which demands further comprehensive studies of multiple disciplines.
2019, 44(6): 1822-1833.
doi: 10.3799/dqkx.2018.385
Abstract:
In the southern part of the Lhasa block in southern Tibet, large-scale zonal distribution of granitic rocks is developed, where the important information on the late subduction of the Neo-Tethys oceanic crust and subsequent collisions and post-collision processes in the Indian-Eurasia continent is recorded. In this paper, LA-ICP-MS zircon U-Pb geochronology, Hf isotope and total trace elements and Sr-Nd isotope geochemical analysis of six granitic rock samples collected in the southern Shannan area of the Lhasa block were obtained. The three-stage zircon ages of~90 Ma, 65 Ma and 23 Ma show that three phases of magmatic activity occurred in the area. The rock samples of the three eras are all subalkalic series, with similar adakite characteristics, enriched with high field strength elements and depleted with large ion lithophile elements. The distribution of rare earth elements is right-dip, geochemical with the feature of arc magma. The zircon εHf(t) of all samples in this paper are positive (+5.6-+14.6), suggesting that they may be derived from the partial melting of the new lower crust. Based on the previous data, the La/Yb ratio of granitic rocks is used to quantitatively show the evolution of crustal thickness in the Shannan area for 100 Ma. From the late Mesozoic, the thickness of the crust in the area was thinned from thick to thin in the Early Cenozoic, and gradually thickened thereafter. This is in line with the changes in the crustal structure caused by the subduction of the Neo-Tethys and the Indian-Eurasia collision-postcollision process since Mesozoic to Cenozoic.
In the southern part of the Lhasa block in southern Tibet, large-scale zonal distribution of granitic rocks is developed, where the important information on the late subduction of the Neo-Tethys oceanic crust and subsequent collisions and post-collision processes in the Indian-Eurasia continent is recorded. In this paper, LA-ICP-MS zircon U-Pb geochronology, Hf isotope and total trace elements and Sr-Nd isotope geochemical analysis of six granitic rock samples collected in the southern Shannan area of the Lhasa block were obtained. The three-stage zircon ages of~90 Ma, 65 Ma and 23 Ma show that three phases of magmatic activity occurred in the area. The rock samples of the three eras are all subalkalic series, with similar adakite characteristics, enriched with high field strength elements and depleted with large ion lithophile elements. The distribution of rare earth elements is right-dip, geochemical with the feature of arc magma. The zircon εHf(t) of all samples in this paper are positive (+5.6-+14.6), suggesting that they may be derived from the partial melting of the new lower crust. Based on the previous data, the La/Yb ratio of granitic rocks is used to quantitatively show the evolution of crustal thickness in the Shannan area for 100 Ma. From the late Mesozoic, the thickness of the crust in the area was thinned from thick to thin in the Early Cenozoic, and gradually thickened thereafter. This is in line with the changes in the crustal structure caused by the subduction of the Neo-Tethys and the Indian-Eurasia collision-postcollision process since Mesozoic to Cenozoic.
2019, 44(6): 1834-1848.
doi: 10.3799/dqkx.2018.397
Abstract:
As the main rock-forming mineral, plagioclase is an effective tool for studying petrogenesis, magma evolution and magma mixing. The cathodoluminescence image, electron probe micro-analysis and LA-ICP-MS composition analysis were carried out for the plagioclase from the granodiorite, monzogranite, diorite dykes and mafic microgranular enclaves (MMEs) in the Quxu batholith in the Gangdese magmatic belt, which can reveal the formation mechanisms and relative magma evolution process of plagioclase complex zoning. The cathodoluminescence images of the plagioclase from the Quxu batholith shows that their color displays a corresponding relationship with the An value. With the decreasing with the An values, the colors are green, blue and dark gray or dark red in turn. The plagioclases have obvious three types of zoning:patchy zonation, sieve texture and oscillatory zoned. The An values of plagioclase from the Quxu granodiorite and monzonite have similar ranges (20-55), while the An values in diorite dikes and MMEs vary widely (25-85), all indicating that the Quxu batholith has undergone a complex opening process. Insitu trace elements analyses show that the granodiorite has similar Sr content (600×10-6-1 100×10-6) with the diorite dykes and MMEs; the Sr content of monzogranite (1 000×10-6-2 400×10-6) is higher than the granodiorite, diorite dykes and MMEs. The above studies show that:the green luminescence of cores and mantle in granodiorite is the result of the mixing of the intermediate magma and felsic magma; the high Sr content of monzogranite is considered to be derived from a Sr-enriched melt. The above studies show that the complex zonings of the plagioclase are the result of the injection of mafic magma into felsic magma. The core of sieve texture plagioclase in diorite vein and MMEs could be xenocrystals, which are captured from the host rocks.
As the main rock-forming mineral, plagioclase is an effective tool for studying petrogenesis, magma evolution and magma mixing. The cathodoluminescence image, electron probe micro-analysis and LA-ICP-MS composition analysis were carried out for the plagioclase from the granodiorite, monzogranite, diorite dykes and mafic microgranular enclaves (MMEs) in the Quxu batholith in the Gangdese magmatic belt, which can reveal the formation mechanisms and relative magma evolution process of plagioclase complex zoning. The cathodoluminescence images of the plagioclase from the Quxu batholith shows that their color displays a corresponding relationship with the An value. With the decreasing with the An values, the colors are green, blue and dark gray or dark red in turn. The plagioclases have obvious three types of zoning:patchy zonation, sieve texture and oscillatory zoned. The An values of plagioclase from the Quxu granodiorite and monzonite have similar ranges (20-55), while the An values in diorite dikes and MMEs vary widely (25-85), all indicating that the Quxu batholith has undergone a complex opening process. Insitu trace elements analyses show that the granodiorite has similar Sr content (600×10-6-1 100×10-6) with the diorite dykes and MMEs; the Sr content of monzogranite (1 000×10-6-2 400×10-6) is higher than the granodiorite, diorite dykes and MMEs. The above studies show that:the green luminescence of cores and mantle in granodiorite is the result of the mixing of the intermediate magma and felsic magma; the high Sr content of monzogranite is considered to be derived from a Sr-enriched melt. The above studies show that the complex zonings of the plagioclase are the result of the injection of mafic magma into felsic magma. The core of sieve texture plagioclase in diorite vein and MMEs could be xenocrystals, which are captured from the host rocks.
2019, 44(6): 1849-1859.
doi: 10.3799/dqkx.2019.043
Abstract:
In order to further constrain the source of the Cuonadong tourmaline granite, Tibet, morphology, chemical and isotopic composition of the tourmaline were studied by means of the microscope, electron probe, laser ablation multi-collector inductively coupled plasma mass spectrometer. The results indicate that the tourmaline from the Cuonadong tourmaline granite belongs to alkali group, and is schorl, which crystallized from boron-rich melts, indicating no obvious boron isotope fractionation between tourmaline and the melts has occurred.δ11B values of the tourmaline from the Cuonadong tourmaline granite range from-6.91‰ to-9.17‰, which are close to the average δ11B value (-10‰ ±3‰) of the continental crust, implying that the Cuonadong tourmaline granite was derived from partial melting of metasedimentay rock. However, δ11B values of the tourmaline from the Cuonadong tourmaline granite is much higher relative to granites derived from metasedimentary rock, and similar to δ11B values of Yardoi leucogranite reported by previous research, which was originated from garnet-amphibolite. Thus, besides metasedimentary rock, there was probably a small amount of garnet-amphibolite present in the source region of the the Cuonadong tourmaline granite.
In order to further constrain the source of the Cuonadong tourmaline granite, Tibet, morphology, chemical and isotopic composition of the tourmaline were studied by means of the microscope, electron probe, laser ablation multi-collector inductively coupled plasma mass spectrometer. The results indicate that the tourmaline from the Cuonadong tourmaline granite belongs to alkali group, and is schorl, which crystallized from boron-rich melts, indicating no obvious boron isotope fractionation between tourmaline and the melts has occurred.δ11B values of the tourmaline from the Cuonadong tourmaline granite range from-6.91‰ to-9.17‰, which are close to the average δ11B value (-10‰ ±3‰) of the continental crust, implying that the Cuonadong tourmaline granite was derived from partial melting of metasedimentay rock. However, δ11B values of the tourmaline from the Cuonadong tourmaline granite is much higher relative to granites derived from metasedimentary rock, and similar to δ11B values of Yardoi leucogranite reported by previous research, which was originated from garnet-amphibolite. Thus, besides metasedimentary rock, there was probably a small amount of garnet-amphibolite present in the source region of the the Cuonadong tourmaline granite.
2019, 44(6): 1860-1875.
doi: 10.3799/dqkx.2018.390
Abstract:
The Nariyongcuo gneiss dome, located to eastern Tethyan Himalaya, consists of many types of granites, containing twomica granite, foliated leucogranites, garnet-bearing leucogranite, garnet-bearing pegmatite, and beryl-bearing pegmatite. All the Nariyongcuo leucogranites are evolved granites and resulted from various degrees of collective fractional crystallization of plagioclase, zircon, monazite, apatite and Ti-rich mineral phases. Comparing with Victorinox value of granites, these granites are enriched in rare metal elements of Bi, Cs, Li, Sn, Be, Pb, B, W, Ta, but relatively depleted in Nb. In addition, the wall rocks are also enriched in rare metal elements. Whole rock geochemical data imply that fractional crystallization and hydrothermal metasomatism resulted in rare metal mineralization within the Nariyongcuo gneiss dome. In the Himalayan belt, high evolved granites are widely distributed, and commonly contain rare metal-bearing minerals (niobite, tapiolite, cassiterite, beryl), suggesting that the Himalaya belt could be another new important target for the exploration of race metal deposits.
The Nariyongcuo gneiss dome, located to eastern Tethyan Himalaya, consists of many types of granites, containing twomica granite, foliated leucogranites, garnet-bearing leucogranite, garnet-bearing pegmatite, and beryl-bearing pegmatite. All the Nariyongcuo leucogranites are evolved granites and resulted from various degrees of collective fractional crystallization of plagioclase, zircon, monazite, apatite and Ti-rich mineral phases. Comparing with Victorinox value of granites, these granites are enriched in rare metal elements of Bi, Cs, Li, Sn, Be, Pb, B, W, Ta, but relatively depleted in Nb. In addition, the wall rocks are also enriched in rare metal elements. Whole rock geochemical data imply that fractional crystallization and hydrothermal metasomatism resulted in rare metal mineralization within the Nariyongcuo gneiss dome. In the Himalayan belt, high evolved granites are widely distributed, and commonly contain rare metal-bearing minerals (niobite, tapiolite, cassiterite, beryl), suggesting that the Himalaya belt could be another new important target for the exploration of race metal deposits.
2019, 44(6): 1876-1887.
doi: 10.3799/dqkx.2018.364
Abstract:
Based on previous findings, in this study we conducted field and indoor investigations. We discusses deposit types, spatial and temporal distribution and associated characteristics, metallogenesis, and future prospecting direction of the metallic ore deposits in western Gangdese metallogenic belt (GMB). The results indicate that the metallic ore deposits (or ore spots) in the GMB are composed mainly of skarn-, porphyry-and epithermal-type deposits. These deposits spatially occur along a W-E trending belt and formed within Mesozoic and Cenozoic. The GMB can be divided into five critical periods according to deposit genesis and dynamic settings, including:(1) copper-gold polymetallic mineralization during Late Triassic to Late Cretaceous associated with Neo-Tethys northward subduction; (2) iron-copper-gold polymetallic mineralization during Middle Jurassic to Early Cretaceous associated with Middle-Tethys southward subduction; (3) copper-gold-molybdenum polymetallic mineralization during early of Late Cretaceous to Late Cretaceous associated with collision between Qiangtang and Lhasa blocks; (4) copper-lead-zinc-silver polymetallic mineralization during late of Late Cretaceous to Eocene associated with collision between Asian and Indian continents; and (5) copper-gold-molybdenum polymetallic mineralization during Miocene associated with extension following collision between Asian and Indian continents. Prominent minerals in the GMB are copper, iron, lead-zinc, gold-silver, etc.
Based on previous findings, in this study we conducted field and indoor investigations. We discusses deposit types, spatial and temporal distribution and associated characteristics, metallogenesis, and future prospecting direction of the metallic ore deposits in western Gangdese metallogenic belt (GMB). The results indicate that the metallic ore deposits (or ore spots) in the GMB are composed mainly of skarn-, porphyry-and epithermal-type deposits. These deposits spatially occur along a W-E trending belt and formed within Mesozoic and Cenozoic. The GMB can be divided into five critical periods according to deposit genesis and dynamic settings, including:(1) copper-gold polymetallic mineralization during Late Triassic to Late Cretaceous associated with Neo-Tethys northward subduction; (2) iron-copper-gold polymetallic mineralization during Middle Jurassic to Early Cretaceous associated with Middle-Tethys southward subduction; (3) copper-gold-molybdenum polymetallic mineralization during early of Late Cretaceous to Late Cretaceous associated with collision between Qiangtang and Lhasa blocks; (4) copper-lead-zinc-silver polymetallic mineralization during late of Late Cretaceous to Eocene associated with collision between Asian and Indian continents; and (5) copper-gold-molybdenum polymetallic mineralization during Miocene associated with extension following collision between Asian and Indian continents. Prominent minerals in the GMB are copper, iron, lead-zinc, gold-silver, etc.
2019, 44(6): 1888-1904.
doi: 10.3799/dqkx.2019.037
Abstract:
In order to gain an in-depth understanding of the tectonic setting of the north and central of Lhasa block, bulk-rock elemental and Sr-Nd-Pb isotopic data for the ore-forming granodiorites of Luobule and Longgeer iron deposit are analyzed and LAICP -MS zircon U -Pb dating result (111.3±1.6 Ma; MSWD=0.61, n=9) for the granodiorite of Luobule deposit.The Luobule and Longgeer ore-forming granodiorites are characterized with high silica (SiO2 contents are 66.63%-69.02% and 64.33%-64.82%, respectively), high alkali (alkali oxides contents are 5.91%-6.40% and 5.81%-6.05%, respectively), but low A/CNK ratios (0.91-0.97 and 0.94-0.95).These intrusive rocks are enriched in LILEs (e.g., Rb、Th、U、K、Pb) while depleted in Ba and HFSEs (e.g., Nb、Ta、Sr、Ti).There have right oblique in chondrite-normalized REE patterns and similar primitive mantle normalized trace element spectrum.In addition, the intrusive granodiorites of Luobule and Longgeer have low ∑ REE (123.11×10-6-148.83×10-6 and 96.17×10-6-101.92×10-6, respectively) and negative Eu anomaly (0.70-0.82 and 0.79-0.81, respectively).The (206Pb/204Pb)t, (207Pb/204Pb)t, (208Pb/204Pb)t, (87Sr/86Sr)i and (143Nd/144Nd)i ratios of whole rock and plagioclase from Longgeer deposit are 18.474 and 18.626, 15.657 and 15.722, 38.592 and 39.145, 0.512 281 and 0.512 339, 0.704 757 6 and 0.707 047 3, respectively.The calculated εNd(t) and tDM2 of the whole rock and plagioclase from Longgeer deposit are -4.13 and -2.99, 1.15 Ga and 1.24 Ga, respectively.In contrast, the (206Pb/204Pb)t, (207Pb/204Pb)t, (208Pb/204Pb)t, (87Sr/86Sr)i, (143Nd/144Nd)i and εNd(t) values of whole rock from Luobule are 18.281, 15.616, 38.369, 0.512 309, 0.706 551 4, -3.62 and 1.20 Ga, respectively.The results above reveal that the ore-forming granodiorites were the product of arc magmatism in late stage of early Cretaceous and were medium -high -K calc-alkaline I-type granite.The primitive magma of the ore-forming plutons were mainly generated by partial melting of crustal materials with the mixing of crust-derived silicic melts and mantle-derived mafic melts and the assimilation of the corresponding wall rocks.Combined with the previous study, by force of contrast the metallogenic event of north and central Lhasa subterrane and southern Qiangtang subterrane, it is propose that there existed extensive magmatism (113±3 Ma) and Fe(-Cu) ore-forming events in north and central Lhasa subterrane are closely related to the break-off of Bangong CoNujiang subducted oceanic crust.
In order to gain an in-depth understanding of the tectonic setting of the north and central of Lhasa block, bulk-rock elemental and Sr-Nd-Pb isotopic data for the ore-forming granodiorites of Luobule and Longgeer iron deposit are analyzed and LAICP -MS zircon U -Pb dating result (111.3±1.6 Ma; MSWD=0.61, n=9) for the granodiorite of Luobule deposit.The Luobule and Longgeer ore-forming granodiorites are characterized with high silica (SiO2 contents are 66.63%-69.02% and 64.33%-64.82%, respectively), high alkali (alkali oxides contents are 5.91%-6.40% and 5.81%-6.05%, respectively), but low A/CNK ratios (0.91-0.97 and 0.94-0.95).These intrusive rocks are enriched in LILEs (e.g., Rb、Th、U、K、Pb) while depleted in Ba and HFSEs (e.g., Nb、Ta、Sr、Ti).There have right oblique in chondrite-normalized REE patterns and similar primitive mantle normalized trace element spectrum.In addition, the intrusive granodiorites of Luobule and Longgeer have low ∑ REE (123.11×10-6-148.83×10-6 and 96.17×10-6-101.92×10-6, respectively) and negative Eu anomaly (0.70-0.82 and 0.79-0.81, respectively).The (206Pb/204Pb)t, (207Pb/204Pb)t, (208Pb/204Pb)t, (87Sr/86Sr)i and (143Nd/144Nd)i ratios of whole rock and plagioclase from Longgeer deposit are 18.474 and 18.626, 15.657 and 15.722, 38.592 and 39.145, 0.512 281 and 0.512 339, 0.704 757 6 and 0.707 047 3, respectively.The calculated εNd(t) and tDM2 of the whole rock and plagioclase from Longgeer deposit are -4.13 and -2.99, 1.15 Ga and 1.24 Ga, respectively.In contrast, the (206Pb/204Pb)t, (207Pb/204Pb)t, (208Pb/204Pb)t, (87Sr/86Sr)i, (143Nd/144Nd)i and εNd(t) values of whole rock from Luobule are 18.281, 15.616, 38.369, 0.512 309, 0.706 551 4, -3.62 and 1.20 Ga, respectively.The results above reveal that the ore-forming granodiorites were the product of arc magmatism in late stage of early Cretaceous and were medium -high -K calc-alkaline I-type granite.The primitive magma of the ore-forming plutons were mainly generated by partial melting of crustal materials with the mixing of crust-derived silicic melts and mantle-derived mafic melts and the assimilation of the corresponding wall rocks.Combined with the previous study, by force of contrast the metallogenic event of north and central Lhasa subterrane and southern Qiangtang subterrane, it is propose that there existed extensive magmatism (113±3 Ma) and Fe(-Cu) ore-forming events in north and central Lhasa subterrane are closely related to the break-off of Bangong CoNujiang subducted oceanic crust.
2019, 44(6): 1905-1922.
doi: 10.3799/dqkx.2018.349
Abstract:
The Bangbule deposit is located in the western part of the Nyainqing Tanggula Pb-Zn-Ag polymetallic metallogenic belt, which is a newly discovered large skarn Pb-Zn-Cu polymetallic deposit in 2010. The magmatic activity in the mining area is relatively simple, with the development of gray-light gray quartz porphyry, which is mainly composed of stock and dyke, and is closely related to the skarn Pb-Zn-Cu mineralization in space and time. In this paper, based on the detailed field basic geological field work and microscopic observation, we study the geochemistry, zircon U-Pb dating, whole rock Sr-Nd-Pb and zircon Hf isotopes of quartz porphyry. The results showed that the LA-ICP-MS U-Pb age of quartz porphyry is 77.2 ±0.8 Ma and 77.3 ±0.7 Ma, which occurred in the Late Cretaceous. The contents of SiO2 in quartz porphyry vary from 72.78% to 77.12%, the contents of K2O are 3.80%~5.55%, and the A/CNK is 0.88-1.18, which showing high-K calc-alkaline, metaluminous and high differentiation I-type granite characteristics. Total REE contents are between 146.89×10-6 and 247.89×10-6, which is characterized by relative enrichment of light rare earth and depletion of heavy rare earth. It has obvious anomalies such as Sr, Eu, Nb, Ta and P, suggesting that the magma experienced an important crystallization differentiation process. The εHf(t) of quartz porphyry is concentrated in the range of -7.92 to -5.73, and the corresponding crustal model is 1 651-1 121 Ma. The (87Sr/86Sr)i and the εNd(t) are 0.714 8-0.725 8 and -9.01 to -7.32, respectively, with the corresponding second Nd model ages (tDM2) of 1 612-1 477 Ma. The lead isotopes show that 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb are 18.686-18.781, 15.699-15.762 and 39.131-39.344, respectively. In summary, the Bangbule quartz porphyry may have been formed by the magma derived from partial melting of the Mesoproterozoic Lhasa block during the extension environment in the post collision after Bangong -Nujiang south subduction. The discovery of the Late Cretaceous quartz porphyry in the Bangbule deposit shows that there is no absolute eruption in the Gangdese belt (80-70 Ma), which suggesting the continuity of the regional magmatic activity.
The Bangbule deposit is located in the western part of the Nyainqing Tanggula Pb-Zn-Ag polymetallic metallogenic belt, which is a newly discovered large skarn Pb-Zn-Cu polymetallic deposit in 2010. The magmatic activity in the mining area is relatively simple, with the development of gray-light gray quartz porphyry, which is mainly composed of stock and dyke, and is closely related to the skarn Pb-Zn-Cu mineralization in space and time. In this paper, based on the detailed field basic geological field work and microscopic observation, we study the geochemistry, zircon U-Pb dating, whole rock Sr-Nd-Pb and zircon Hf isotopes of quartz porphyry. The results showed that the LA-ICP-MS U-Pb age of quartz porphyry is 77.2 ±0.8 Ma and 77.3 ±0.7 Ma, which occurred in the Late Cretaceous. The contents of SiO2 in quartz porphyry vary from 72.78% to 77.12%, the contents of K2O are 3.80%~5.55%, and the A/CNK is 0.88-1.18, which showing high-K calc-alkaline, metaluminous and high differentiation I-type granite characteristics. Total REE contents are between 146.89×10-6 and 247.89×10-6, which is characterized by relative enrichment of light rare earth and depletion of heavy rare earth. It has obvious anomalies such as Sr, Eu, Nb, Ta and P, suggesting that the magma experienced an important crystallization differentiation process. The εHf(t) of quartz porphyry is concentrated in the range of -7.92 to -5.73, and the corresponding crustal model is 1 651-1 121 Ma. The (87Sr/86Sr)i and the εNd(t) are 0.714 8-0.725 8 and -9.01 to -7.32, respectively, with the corresponding second Nd model ages (tDM2) of 1 612-1 477 Ma. The lead isotopes show that 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb are 18.686-18.781, 15.699-15.762 and 39.131-39.344, respectively. In summary, the Bangbule quartz porphyry may have been formed by the magma derived from partial melting of the Mesoproterozoic Lhasa block during the extension environment in the post collision after Bangong -Nujiang south subduction. The discovery of the Late Cretaceous quartz porphyry in the Bangbule deposit shows that there is no absolute eruption in the Gangdese belt (80-70 Ma), which suggesting the continuity of the regional magmatic activity.
2019, 44(6): 1923-1934.
doi: 10.3799/dqkx.2019.077
Abstract:
We present Mo and Cu isotope of molybdenite and chalcopyrite from two porphyry deposits (Qulong, Dabu) and one quartz-molybdenite vein -type deposit (Jigongcun) along the Gangdese metallogenic belt in the Tibetan Plateau.The results show that the range of δ65/63Cu in the Gangdese porphyry deposit in Tibet is between +0.01‰-+0.98‰, and the range of δ97/95Mo is between -0.34‰ to -0.15‰.The δ97/95Mo of molybdenum in the quartz-molybdenite vein-type deposit is obviously lighter, and cluster from -0.35 ‰ to -0.23‰. Two types porphyry deposits produced in different tectonic settings from the island arc and collisional orogenic belt, it is found that they have similar range of δ65/63Cu in chalcopyrite, all of which are characterized by unimodal distribution; In contrast, the hydrothermal veins and ore-bearing porphyry from the Qulong porphyry deposit have a similar range of δ65/63Cu in chalcopyrite, which suggest that the origin of Cu is consistent. In addition, in the collisional orogenic belt porphyry deposit, different alteration zones have different Cu, Mo isotopic compositions, and from the center outward of the the alteration zone, Cu-Mo isotopic has a certain negative correlation, and this relationship have close relationship with the property of mineral fluid. Comparing the range of δ97/95Mo of the quartz vein type and porphyry type of deposits in the Gangdese area, it is found that the former has a lower δ97/95Mo, which may suggest that the ore sources of the two types of deposits are consistent.
We present Mo and Cu isotope of molybdenite and chalcopyrite from two porphyry deposits (Qulong, Dabu) and one quartz-molybdenite vein -type deposit (Jigongcun) along the Gangdese metallogenic belt in the Tibetan Plateau.The results show that the range of δ65/63Cu in the Gangdese porphyry deposit in Tibet is between +0.01‰-+0.98‰, and the range of δ97/95Mo is between -0.34‰ to -0.15‰.The δ97/95Mo of molybdenum in the quartz-molybdenite vein-type deposit is obviously lighter, and cluster from -0.35 ‰ to -0.23‰. Two types porphyry deposits produced in different tectonic settings from the island arc and collisional orogenic belt, it is found that they have similar range of δ65/63Cu in chalcopyrite, all of which are characterized by unimodal distribution; In contrast, the hydrothermal veins and ore-bearing porphyry from the Qulong porphyry deposit have a similar range of δ65/63Cu in chalcopyrite, which suggest that the origin of Cu is consistent. In addition, in the collisional orogenic belt porphyry deposit, different alteration zones have different Cu, Mo isotopic compositions, and from the center outward of the the alteration zone, Cu-Mo isotopic has a certain negative correlation, and this relationship have close relationship with the property of mineral fluid. Comparing the range of δ97/95Mo of the quartz vein type and porphyry type of deposits in the Gangdese area, it is found that the former has a lower δ97/95Mo, which may suggest that the ore sources of the two types of deposits are consistent.
2019, 44(6): 1935-1956.
doi: 10.3799/dqkx.2018.370
Abstract:
The current studies of the deposits in the Gangdese metallogenic belt is predominate in the eastern section, but the new discovered Luerma porphyry copper (gold) Deposit belongs to the western segment of Gangdise polymetallic metallogenic belt. The Luerma copper (gold) deposit developed typical porphyry deposits'hydrothermal alteration zones, which are divided as potassium-silicification zone, sericitization zone, clayization zone, and propylitization-propylitization zone from proximal to distal, respectively. Hornfels and malachite are also generally distributed in the mining area. Moreover, three main types of hydrothermal veins have been identified based on its mineral assemblages, cutting relationship and alteration features, which consist of the potassium-silicification vein (A vein), the medium-term quartz-polymetallic sulfides vein (B vein), and the epidote-carbonatation (D vein), respectively. Petrographic, microthermometric, laser Raman microprobe and H -O -C results of fluid inclusions in different hydrothermal veins. Fluid inclusions of A vein's homogenization temperatures, and salinities vary from 390~460℃, 4.5%~21.6% NaCleqv, 43.6%~59.6% NaCleqv, respectively; fluid inclusions of B vein's homogenization temperatures, and salinities, vary from 310~380℃, 3.6%~19.8% NaCleqv, 6.0%~16.0% NaCleqv, respectively; fluid inclusions of D vein's homogenization temperatures, and salinities, vary from 200~320℃, 0.4%~14.7% NaCleqv, 0.70~1.00 g/cm3, respectively. And the carbon, hydrogen, oxygen isotope test results reveals that the δDH2O, V-SMOW values of fluid inclusions in quartz veins range from -128‰ to -100‰, and δ18OH2O, V-SMOW values of fluid inclusions in quartz veins range from -9.09 ‰ to -1.45‰, the δ13CCal, V-PDB values of calcite veins range from -20.8‰ to -19.9‰, and δ18OCal, V-SMOW values of calcite veins range 9.4‰ to 10.5‰, indicating a feature of magmatic hydrothermal, but may mixtured geothermal water in late stage. In brief, the ore-forming fluid of the Luerma copper (gold) deposit is a Ca+-Na+-Cl-H2O fluid system, with high contents of CO2, N2, and CH4, high homogenization temperature, high salinity and, low-moderate density, rich in metallic elements as Cu, Fe, and Mo et al., which characteristics similar to typical porphyry copper deposits. These studies suggest that, the luerma copper ore ore-forming fluid moved from the deep closed system to the shallow open system and broke through the critical state of decompressing boiling rapidly, which occurred phase separation resulting in the precipitation of metal sulfide, forming A vein and B vein type mineralization. Afterwards, as the heavy precipitation of minerals in ore bearing hydrothermal fluid, and the mixing of atmospheric precipitation, et al., the temperature and salinity of the fluid decreased rapidly, resulting in D vein mineralization.
The current studies of the deposits in the Gangdese metallogenic belt is predominate in the eastern section, but the new discovered Luerma porphyry copper (gold) Deposit belongs to the western segment of Gangdise polymetallic metallogenic belt. The Luerma copper (gold) deposit developed typical porphyry deposits'hydrothermal alteration zones, which are divided as potassium-silicification zone, sericitization zone, clayization zone, and propylitization-propylitization zone from proximal to distal, respectively. Hornfels and malachite are also generally distributed in the mining area. Moreover, three main types of hydrothermal veins have been identified based on its mineral assemblages, cutting relationship and alteration features, which consist of the potassium-silicification vein (A vein), the medium-term quartz-polymetallic sulfides vein (B vein), and the epidote-carbonatation (D vein), respectively. Petrographic, microthermometric, laser Raman microprobe and H -O -C results of fluid inclusions in different hydrothermal veins. Fluid inclusions of A vein's homogenization temperatures, and salinities vary from 390~460℃, 4.5%~21.6% NaCleqv, 43.6%~59.6% NaCleqv, respectively; fluid inclusions of B vein's homogenization temperatures, and salinities, vary from 310~380℃, 3.6%~19.8% NaCleqv, 6.0%~16.0% NaCleqv, respectively; fluid inclusions of D vein's homogenization temperatures, and salinities, vary from 200~320℃, 0.4%~14.7% NaCleqv, 0.70~1.00 g/cm3, respectively. And the carbon, hydrogen, oxygen isotope test results reveals that the δDH2O, V-SMOW values of fluid inclusions in quartz veins range from -128‰ to -100‰, and δ18OH2O, V-SMOW values of fluid inclusions in quartz veins range from -9.09 ‰ to -1.45‰, the δ13CCal, V-PDB values of calcite veins range from -20.8‰ to -19.9‰, and δ18OCal, V-SMOW values of calcite veins range 9.4‰ to 10.5‰, indicating a feature of magmatic hydrothermal, but may mixtured geothermal water in late stage. In brief, the ore-forming fluid of the Luerma copper (gold) deposit is a Ca+-Na+-Cl-H2O fluid system, with high contents of CO2, N2, and CH4, high homogenization temperature, high salinity and, low-moderate density, rich in metallic elements as Cu, Fe, and Mo et al., which characteristics similar to typical porphyry copper deposits. These studies suggest that, the luerma copper ore ore-forming fluid moved from the deep closed system to the shallow open system and broke through the critical state of decompressing boiling rapidly, which occurred phase separation resulting in the precipitation of metal sulfide, forming A vein and B vein type mineralization. Afterwards, as the heavy precipitation of minerals in ore bearing hydrothermal fluid, and the mixing of atmospheric precipitation, et al., the temperature and salinity of the fluid decreased rapidly, resulting in D vein mineralization.
2019, 44(6): 1957-1973.
doi: 10.3799/dqkx.2019.041
Abstract:
The Lietinggang-Leqingla deposit developed Pb-Zn-Fe-Cu-Mo five kinds of metals in the same ore district, which is the most typical skarn-type deposit in the north Gangdese polymetallic belt.Studying on the ore fluid property is helpful for us to solve the ore-forming mechanism of this deposit, which is considered to be polymetallic symbiosis deposit with different source attributes. In this study, skarn minerals and gangue minerals closely related to Fe-Cu-Mo and Pb-Zn-Cu mineralization were sampled and a detailed study with regard to fluid inclusion and C-H-O isotopes was conducted, the results show that the fluid source and evolution process of the ore blocks are similar. There are mainly liquid-rich fluid inclusions in the sakrn alteration stage, and fluid in this stage has high temperatures and medium -high salinities.There are mainly liquid -rich fluid inclusion and daughter mineral-bearing fluid inclusions in the quartz-sulfide stage and carbonate stage, fluid in the quartz-sulfide stage has medium-high temperature, and salinity can be divided into high salinity and low salinity.Fluid in the carbonate stage has medium-low temperature, and salinity also can be devided into high salinity and low salinity. Studies show that the presence of two fluids with very different salinity results from boiling of the ore-forming fluid. Stable isotope compositions indicate that the ore-forming fluids were derived from magmatic hydrothermal fluid which had undergone degasification in skarn alteration stage and was mixed with meteoric water in quartz sulfide stage and carbonate stage. The δ18O is obviously depleted in the limestone strata compare with the normal marine limestone, which indicate that the ore-forming fluid had large-scale migration and water-rock interaction in the whole limestone strata of ore district, thus the Pb-Zn-Cu mineralization is formed in the distal skarn belt. This study, combined with previously published data, Fe-Cu and Pb-Zn mineralization of the Lietinggang-Leqingla deposit are the products of magmatic activities in the same period, but they are related to magma of different attributes. Cooling, fluid mixing and variation of pH of ore-forming fluid resulted in the precipitation of metal of the Lietinggang-Leqingla deposit, the mineralization zoning from the Lietinggang-Leqingla deposit was mostly like controlled by the difference of metallogenic temperature and magmatic attribute.
The Lietinggang-Leqingla deposit developed Pb-Zn-Fe-Cu-Mo five kinds of metals in the same ore district, which is the most typical skarn-type deposit in the north Gangdese polymetallic belt.Studying on the ore fluid property is helpful for us to solve the ore-forming mechanism of this deposit, which is considered to be polymetallic symbiosis deposit with different source attributes. In this study, skarn minerals and gangue minerals closely related to Fe-Cu-Mo and Pb-Zn-Cu mineralization were sampled and a detailed study with regard to fluid inclusion and C-H-O isotopes was conducted, the results show that the fluid source and evolution process of the ore blocks are similar. There are mainly liquid-rich fluid inclusions in the sakrn alteration stage, and fluid in this stage has high temperatures and medium -high salinities.There are mainly liquid -rich fluid inclusion and daughter mineral-bearing fluid inclusions in the quartz-sulfide stage and carbonate stage, fluid in the quartz-sulfide stage has medium-high temperature, and salinity can be divided into high salinity and low salinity.Fluid in the carbonate stage has medium-low temperature, and salinity also can be devided into high salinity and low salinity. Studies show that the presence of two fluids with very different salinity results from boiling of the ore-forming fluid. Stable isotope compositions indicate that the ore-forming fluids were derived from magmatic hydrothermal fluid which had undergone degasification in skarn alteration stage and was mixed with meteoric water in quartz sulfide stage and carbonate stage. The δ18O is obviously depleted in the limestone strata compare with the normal marine limestone, which indicate that the ore-forming fluid had large-scale migration and water-rock interaction in the whole limestone strata of ore district, thus the Pb-Zn-Cu mineralization is formed in the distal skarn belt. This study, combined with previously published data, Fe-Cu and Pb-Zn mineralization of the Lietinggang-Leqingla deposit are the products of magmatic activities in the same period, but they are related to magma of different attributes. Cooling, fluid mixing and variation of pH of ore-forming fluid resulted in the precipitation of metal of the Lietinggang-Leqingla deposit, the mineralization zoning from the Lietinggang-Leqingla deposit was mostly like controlled by the difference of metallogenic temperature and magmatic attribute.
2019, 44(6): 1974-1986.
doi: 10.3799/dqkx.2019.066
Abstract:
Jiagangxueshan W-Mo deposit, Shenzha County, is the first greisen-type W deposit in Tibet. Studying the deposit is of great significance in the regional metallogenic mechanism and prospecting. The mineralization is strongly linked with the monzogranite located in the center of the deposit, and ores usually occur in inner monzogranite or sedimentary wall rocks that are adjacent to the monzogranite. The orebody types of the deposit contain greisen-type and quartz vein-type. The majority of ores distribute in greisens and intensively greisenized monzogranites in the form of veinlets or dissemination, while the minority mainly precipitated in the sedimentary wall rocks, presenting as wide quartz veins. To investigate the sources of ore -forming fluids and materials of Jiagangxueshan W -Mo deposit, wolframites and quartzs, metal sulfides from greisen-and quartz vein-type orebodies are sellected for H, O and S-Pb isotope analysis, respectively. δ18OV-SMOW (‰) values of wolframite of the deposit range from 3.7-4.7. The hydrogen and oxygen isotope compositions of the quartzs selected from ores show that the δ18Owater values of quartzs are ranging from 2.0‰-4.3‰, with the δD values range from -131‰ to -84‰. The H-O data indicate that ore-forming fluids were derived from residual magma water after degassing. δ34S values of the sulfides range from +2.2‰ to +5.3‰, indicative of a magmatic source of sulfur. The values of 206Pb/204Pb、207Pb/204Pb、208Pb/204Pb are 18.582 2-18.797 1、15.671 7-15.760 6、39.462 5-39.501 2, respectively, which further show that the ore-forming materials were derived from Precambrian metamorphic basement of the central Lhasa subterrane.
Jiagangxueshan W-Mo deposit, Shenzha County, is the first greisen-type W deposit in Tibet. Studying the deposit is of great significance in the regional metallogenic mechanism and prospecting. The mineralization is strongly linked with the monzogranite located in the center of the deposit, and ores usually occur in inner monzogranite or sedimentary wall rocks that are adjacent to the monzogranite. The orebody types of the deposit contain greisen-type and quartz vein-type. The majority of ores distribute in greisens and intensively greisenized monzogranites in the form of veinlets or dissemination, while the minority mainly precipitated in the sedimentary wall rocks, presenting as wide quartz veins. To investigate the sources of ore -forming fluids and materials of Jiagangxueshan W -Mo deposit, wolframites and quartzs, metal sulfides from greisen-and quartz vein-type orebodies are sellected for H, O and S-Pb isotope analysis, respectively. δ18OV-SMOW (‰) values of wolframite of the deposit range from 3.7-4.7. The hydrogen and oxygen isotope compositions of the quartzs selected from ores show that the δ18Owater values of quartzs are ranging from 2.0‰-4.3‰, with the δD values range from -131‰ to -84‰. The H-O data indicate that ore-forming fluids were derived from residual magma water after degassing. δ34S values of the sulfides range from +2.2‰ to +5.3‰, indicative of a magmatic source of sulfur. The values of 206Pb/204Pb、207Pb/204Pb、208Pb/204Pb are 18.582 2-18.797 1、15.671 7-15.760 6、39.462 5-39.501 2, respectively, which further show that the ore-forming materials were derived from Precambrian metamorphic basement of the central Lhasa subterrane.
2019, 44(6): 1987-1997.
doi: 10.3799/dqkx.2018.358
Abstract:
Huoshaoyun is a newly discovered world-class nonsulfide zinc-lead deposit in Xinjiang, NW China, so its genesis attracts many geologists'attentions. Conformable orebodies in the deposit contain massive and minor stratiform and breccia-hosted ores that are dominated by smithsonite and cerussite. Ores are hosted by Middle Jurassic sedimentary gypsum-bearing platform facies carbonate. Clearly, the carbonate is typical host for Mississippi Valley-type (MVT) deposit rather than for sedimentary exhalative (SEDEX) deposit. Galena is common in the ores and was replaced by cerussite, implying that precursor mineralization in the deposit was zinc and lead sulfides. δ34SV-CDT values of the galena range from -34‰ to -18‰, indicating that derivation of reduced sulfur was related to bacterial sulfate reduction (BSR) process, which is common in MVT deposits but is scarce in magmatic -related Zn -Pb deposits. Together with the absence of magmatic -related hydrothermal alteration and mineralization, it suggests that primary mineralization at Huoshaoyun is of MVT origin. Oxygen isotopic compositions of water that reached isotopic equilibrium with smithsonite and cerussite are low in temperature and light in δ18O values, implyimg that meteoric water was involved in the two mineral formations. Combined with the observation that galena was replaced by cerussite, we suggest that the smithsonite and cerussite were the result of intensive supergene oxidization of primary znic and lead sulfides of MVT origin.
Huoshaoyun is a newly discovered world-class nonsulfide zinc-lead deposit in Xinjiang, NW China, so its genesis attracts many geologists'attentions. Conformable orebodies in the deposit contain massive and minor stratiform and breccia-hosted ores that are dominated by smithsonite and cerussite. Ores are hosted by Middle Jurassic sedimentary gypsum-bearing platform facies carbonate. Clearly, the carbonate is typical host for Mississippi Valley-type (MVT) deposit rather than for sedimentary exhalative (SEDEX) deposit. Galena is common in the ores and was replaced by cerussite, implying that precursor mineralization in the deposit was zinc and lead sulfides. δ34SV-CDT values of the galena range from -34‰ to -18‰, indicating that derivation of reduced sulfur was related to bacterial sulfate reduction (BSR) process, which is common in MVT deposits but is scarce in magmatic -related Zn -Pb deposits. Together with the absence of magmatic -related hydrothermal alteration and mineralization, it suggests that primary mineralization at Huoshaoyun is of MVT origin. Oxygen isotopic compositions of water that reached isotopic equilibrium with smithsonite and cerussite are low in temperature and light in δ18O values, implyimg that meteoric water was involved in the two mineral formations. Combined with the observation that galena was replaced by cerussite, we suggest that the smithsonite and cerussite were the result of intensive supergene oxidization of primary znic and lead sulfides of MVT origin.
2019, 44(6): 1998-2016.
doi: 10.3799/dqkx.2019.122
Abstract:
The genesis of Mazhala Au-Sb deposit, which is one of the most important Au-Sb deposits in South Tibet Au-Sb metallogenic belt, is still open to debate. Based on field observation, petrography, microscopy, fluid inclusions, and stable isotopic results, in this paper, it discusses the characteristics of ore-forming fluid, the transportation, and the precipitation mechanism of Au and Sb. It can be concluded that the ore-formng fluid has a dominant magmatic origin, and is of moderate temperature (ca.255℃), low salinity (ca.2.8%-3.5% NaCleqv) and rich in CO2. The estimated ore-forming pressure is about 150 MPa. The unmixing between CO2 and aqueous during the fluid evolution leads to the ore precipitation. The Au, Sb may have been sourced from wall rocks, especially the submarine volcanic rock of them.
The genesis of Mazhala Au-Sb deposit, which is one of the most important Au-Sb deposits in South Tibet Au-Sb metallogenic belt, is still open to debate. Based on field observation, petrography, microscopy, fluid inclusions, and stable isotopic results, in this paper, it discusses the characteristics of ore-forming fluid, the transportation, and the precipitation mechanism of Au and Sb. It can be concluded that the ore-formng fluid has a dominant magmatic origin, and is of moderate temperature (ca.255℃), low salinity (ca.2.8%-3.5% NaCleqv) and rich in CO2. The estimated ore-forming pressure is about 150 MPa. The unmixing between CO2 and aqueous during the fluid evolution leads to the ore precipitation. The Au, Sb may have been sourced from wall rocks, especially the submarine volcanic rock of them.
2019, 44(6): 2017-2038.
doi: 10.3799/dqkx.2018.380
Abstract:
Sefu deposit is a newly discovered Au-Cu deposit in Gangdese porphyry Cu belt. Its Au orebodies are epithermal type and superimposed on the vein type Cu orebodies. According to detailed geological survey, five periods of hydrothermal activity are distinguished in and around Sefu and Jigongxi. They are Early Eocene magnetite mineralization, Late Eocene-Early Oligocene ductile shearing related one, Early Miocene molybdenum and copper mineralization, and gold mineralization at last. Petrography, microthermometry, laser Raman spectroscopy together with hydrogen and oxygen isotope analysis are conducted on the fluid inclusions in quartz formed during these five periods. It is found that fluid related to magnetite mineralization is the mixture of magma originated aqueous fluid of high temperature, high pressure, high salinity, and formation water. Fluid related to molybdenum mineralization is the mixture of meteoric water and magma originated aqueous fluid of high temperature, high pressure, and high salinity. Fluid related to copper mineralization is the mixture of medium-high temperature, low salinity fluid and containing medium density CO2, which was originated from magma, and low temperature, low salinity fluid which is from meteoric water. Fluid related to gold mineralization is the mixture of medium temperature, low salinity fluid with low density CO2, CH4 and N2, which was originated from magma, and medium temperature, low salinity fluid, which is from meteoric water. Estimation results of trapping temperature and pressure based on microthermometry also show 1.5-4.1 km erosion had happened before molybdenum and copper mineralization, and 6 km erosion had happened before gold mineralization. After gold mineralization, 0.8-1.2 km erosion had happened. Exploration should focus more on gold orebodies in the near north-south striking faults in Sefu area in future.
Sefu deposit is a newly discovered Au-Cu deposit in Gangdese porphyry Cu belt. Its Au orebodies are epithermal type and superimposed on the vein type Cu orebodies. According to detailed geological survey, five periods of hydrothermal activity are distinguished in and around Sefu and Jigongxi. They are Early Eocene magnetite mineralization, Late Eocene-Early Oligocene ductile shearing related one, Early Miocene molybdenum and copper mineralization, and gold mineralization at last. Petrography, microthermometry, laser Raman spectroscopy together with hydrogen and oxygen isotope analysis are conducted on the fluid inclusions in quartz formed during these five periods. It is found that fluid related to magnetite mineralization is the mixture of magma originated aqueous fluid of high temperature, high pressure, high salinity, and formation water. Fluid related to molybdenum mineralization is the mixture of meteoric water and magma originated aqueous fluid of high temperature, high pressure, and high salinity. Fluid related to copper mineralization is the mixture of medium-high temperature, low salinity fluid and containing medium density CO2, which was originated from magma, and low temperature, low salinity fluid which is from meteoric water. Fluid related to gold mineralization is the mixture of medium temperature, low salinity fluid with low density CO2, CH4 and N2, which was originated from magma, and medium temperature, low salinity fluid, which is from meteoric water. Estimation results of trapping temperature and pressure based on microthermometry also show 1.5-4.1 km erosion had happened before molybdenum and copper mineralization, and 6 km erosion had happened before gold mineralization. After gold mineralization, 0.8-1.2 km erosion had happened. Exploration should focus more on gold orebodies in the near north-south striking faults in Sefu area in future.
2019, 44(6): 2039-2051.
doi: 10.3799/dqkx.2018.379
Abstract:
The Nianzha gold deposit, located in the central section of the Yurlung-Zangbo suture zone is a large orogenic gold deposit which occurred in a fracture zone bordered by altered diorite in the hanging wall to the north and the Renbu tectonic mélange in the footwall to the south. In this paper, it combines zircon U-Pb, (U-Th)/He and apatite fission track dating of the fresh and mineralized diorite in order to restrict the cooling and denudation history of the Nianzha deposit. The results show that the zircon U-Pb age of the fresh diorite is (46.32±0.53) Ma and zircon (U-Th)/He ages of fresh diorite is between (7.14 ±0.24) Ma and (9.80 ±0.27) Ma, and the zircon (U-Th)/He ages of the mineralized diorite are between (8.38±0.24) Ma and (11.19±0.31) Ma. The apatite fission track ages of two mineralization diorite are (5.9±0.5) Ma and (5.3±1.0) Ma respectively. Since the consolidation of the diorite, the Nianzha gold deposit has experienced two rapid cooling processes:the first process started from 46.3 Ma to 43.6 Ma, and the temperature dropped from 750℃ to 350℃ with the cooling rate of about 148℃/Ma, while the second process happened between 8.5~2.0 Ma with the temperature dropped from 200℃ to 30℃ with cooling rate of about 26℃/Ma. The mineralization depth of the Nianzha deposit is about 9.7 km; at 8.5 Ma, the deposit was uplifted to 4.6 km; from 8.5 to 5.6 Ma, the deposit are uplifted to 2.8 km; and from 5.6 to 2.0 Ma, the Nianzha deposit was exfoliated to the surface.
The Nianzha gold deposit, located in the central section of the Yurlung-Zangbo suture zone is a large orogenic gold deposit which occurred in a fracture zone bordered by altered diorite in the hanging wall to the north and the Renbu tectonic mélange in the footwall to the south. In this paper, it combines zircon U-Pb, (U-Th)/He and apatite fission track dating of the fresh and mineralized diorite in order to restrict the cooling and denudation history of the Nianzha deposit. The results show that the zircon U-Pb age of the fresh diorite is (46.32±0.53) Ma and zircon (U-Th)/He ages of fresh diorite is between (7.14 ±0.24) Ma and (9.80 ±0.27) Ma, and the zircon (U-Th)/He ages of the mineralized diorite are between (8.38±0.24) Ma and (11.19±0.31) Ma. The apatite fission track ages of two mineralization diorite are (5.9±0.5) Ma and (5.3±1.0) Ma respectively. Since the consolidation of the diorite, the Nianzha gold deposit has experienced two rapid cooling processes:the first process started from 46.3 Ma to 43.6 Ma, and the temperature dropped from 750℃ to 350℃ with the cooling rate of about 148℃/Ma, while the second process happened between 8.5~2.0 Ma with the temperature dropped from 200℃ to 30℃ with cooling rate of about 26℃/Ma. The mineralization depth of the Nianzha deposit is about 9.7 km; at 8.5 Ma, the deposit was uplifted to 4.6 km; from 8.5 to 5.6 Ma, the deposit are uplifted to 2.8 km; and from 5.6 to 2.0 Ma, the Nianzha deposit was exfoliated to the surface.
2019, 44(6): 2052-2062.
doi: 10.3799/dqkx.2018.361
Abstract:
The Bangbu deposit is the only large orogenic gold deposit that is being exploited with the highest degree of research in the Yurlung-Zangbo suture zone. In order to understand the source, transportation and precipitation of Au in the Bangbu deposit, in situ microanalysis technique was used to obtain the trace elements compositions of Au-bearing pyrite from different generations. In situ trace elements results show that the siderophile elements Co and Ni mainly enter the lattice of pyrite to substitute Fe while As and Se substitute S in the form of isomorphism. Gold is distributed evenly in different generations of pyrite in the form of nanoparticles. The Co/Ni ratios of pyrite from three generations of Au-bearing quartz veins are all less than 1 which preserve the information of pyrite of the surrounding rocks indicating a kind of sedimentation or sedimentation-reformation origin. As and Se play important roles in the migration and accumulation of Au as Au has obvious positive correlation with As and Se.
The Bangbu deposit is the only large orogenic gold deposit that is being exploited with the highest degree of research in the Yurlung-Zangbo suture zone. In order to understand the source, transportation and precipitation of Au in the Bangbu deposit, in situ microanalysis technique was used to obtain the trace elements compositions of Au-bearing pyrite from different generations. In situ trace elements results show that the siderophile elements Co and Ni mainly enter the lattice of pyrite to substitute Fe while As and Se substitute S in the form of isomorphism. Gold is distributed evenly in different generations of pyrite in the form of nanoparticles. The Co/Ni ratios of pyrite from three generations of Au-bearing quartz veins are all less than 1 which preserve the information of pyrite of the surrounding rocks indicating a kind of sedimentation or sedimentation-reformation origin. As and Se play important roles in the migration and accumulation of Au as Au has obvious positive correlation with As and Se.
2019, 44(6): 2063-2083.
doi: 10.3799/dqkx.2019.125
Abstract:
Newly-determined zircon U-Pb ages, whole rock major and trace elements, Sr-Nd-Pb and zircon Hf isotope data, are used to firstly examine the geochemical characteristics of the ore-related syenite porphyry and trachyte in the Yao' an Au-Pb-Ag deposit, western Yunnan, and then to systematically discuss the origin and evolution processes of the parental magmas in this paper. The zircon U -Pb ages of the syenite porphyry and trachyte in the Yao' an Au -Pb -Ag deposit respectively are 33.8±0.42 Ma and 33.9±0.60 Ma. And their patterns of trace elements and REE, and the Sr-Nd-Pb isotopes, are very similar to the contemporary mafic volcanic rocks and lamprophyre from the western Yunnan, but obviously different from the contemporary alkali-rich adakitic rocks in the western Yangtze craton. The relationships of SiO2 contents with major and trace element contents of the whole-rocks indicate that magmas for the syenite porphyry and trachyte could be formed by differentiation of the contemporary mafic magmas in the diggings. This implies that syenite porphyry and trachyte may have similar source to the mafic magmas. High Rb/Sr(≥ 0.1) and low Ba/Rb(< 20) ratios of the syenite porphyry and trachyte indicate that they were derived from a metasomatized enriched mantle source with abundant phlogopite. And the low εHf and the old model age of the rocks indicate that the metasomatism of the source region might happen in Mesoproterozoic. The alkali-rich magmation in Yao' an is closely related with the mineralization. The syenite porphyry and trachyte of Yao' an have a higher initial Pb isotopic composition than the mafic volcanic rocks and lamprophyre from the western Yunnan, which implies that some degrees of the crustal contamination might occur during evolution process of the magmas which could increase the metal contents of the magma and enhance the mineralization potential of the magmas. The moderate oxygen fugacity of the magmas in favour of the Au enrichment. And the obvious fractional crystallization of hornblende and the formation of abundant biotite indicate that the primary magmas were very hydrous, which facilitated the formation of oreforming fluids. All of these features could provide advantageous conditions for the mineralization in the Yao' an deposit.
Newly-determined zircon U-Pb ages, whole rock major and trace elements, Sr-Nd-Pb and zircon Hf isotope data, are used to firstly examine the geochemical characteristics of the ore-related syenite porphyry and trachyte in the Yao' an Au-Pb-Ag deposit, western Yunnan, and then to systematically discuss the origin and evolution processes of the parental magmas in this paper. The zircon U -Pb ages of the syenite porphyry and trachyte in the Yao' an Au -Pb -Ag deposit respectively are 33.8±0.42 Ma and 33.9±0.60 Ma. And their patterns of trace elements and REE, and the Sr-Nd-Pb isotopes, are very similar to the contemporary mafic volcanic rocks and lamprophyre from the western Yunnan, but obviously different from the contemporary alkali-rich adakitic rocks in the western Yangtze craton. The relationships of SiO2 contents with major and trace element contents of the whole-rocks indicate that magmas for the syenite porphyry and trachyte could be formed by differentiation of the contemporary mafic magmas in the diggings. This implies that syenite porphyry and trachyte may have similar source to the mafic magmas. High Rb/Sr(≥ 0.1) and low Ba/Rb(< 20) ratios of the syenite porphyry and trachyte indicate that they were derived from a metasomatized enriched mantle source with abundant phlogopite. And the low εHf and the old model age of the rocks indicate that the metasomatism of the source region might happen in Mesoproterozoic. The alkali-rich magmation in Yao' an is closely related with the mineralization. The syenite porphyry and trachyte of Yao' an have a higher initial Pb isotopic composition than the mafic volcanic rocks and lamprophyre from the western Yunnan, which implies that some degrees of the crustal contamination might occur during evolution process of the magmas which could increase the metal contents of the magma and enhance the mineralization potential of the magmas. The moderate oxygen fugacity of the magmas in favour of the Au enrichment. And the obvious fractional crystallization of hornblende and the formation of abundant biotite indicate that the primary magmas were very hydrous, which facilitated the formation of oreforming fluids. All of these features could provide advantageous conditions for the mineralization in the Yao' an deposit.
2019, 44(6): 2084-2105.
doi: 10.3799/dqkx.2019.020
Abstract:
Deep seismic reflection profile has been used as the pioneering technology in the study of lithosphere fine structure because of its high detection accuracy and also has played an important role in the structural detection of typical mining areas around the world. In order to study the deep structure and the metallogenic process of the collision orogenic metallogenic system on the Qinghai-Tibet plateau, in this paper, the development status of deep seismic reflection technology is summarized systematically, and the application cases of this technology in typical ore concentration areas in Canada, Australia, China, Russia and Sweden are combed. The influences of deep crust structure on ore-controlling factors in ore centration areas and the relationships between the structure of crust and upper mantle at depth and the deep metallogenic process are illustrated. According to the global examples, the detection results of deep seismic reflection profile provide deep clues for the formation of large ore concentrated areas. The reflective transparent zone may be the upward migration channel of the mantle fluid, forming the mineral and energy sources of ore concentration area, indicating that the mantle material is involved in mineralization. Fracture systems characterized by strong reflectivity, including large-scale faults, detachments and crustal shear zones, are pathways through which metallogenic fluids migrate upward from the lower crust. The"bright spot"in the deep seismic reflection profiles of ore concentrated areas may be the reflection of the residual magma chamber formed after the deep magma of volcanic activity surges into the middle crust. Revealing the deep fine structure not only plays an important role in the reconstruction of the tectonic historical evolution of ore concentration area, but also has crucial guiding significance for the determination of the future metallogenic potential and the target area of the foreground.
Deep seismic reflection profile has been used as the pioneering technology in the study of lithosphere fine structure because of its high detection accuracy and also has played an important role in the structural detection of typical mining areas around the world. In order to study the deep structure and the metallogenic process of the collision orogenic metallogenic system on the Qinghai-Tibet plateau, in this paper, the development status of deep seismic reflection technology is summarized systematically, and the application cases of this technology in typical ore concentration areas in Canada, Australia, China, Russia and Sweden are combed. The influences of deep crust structure on ore-controlling factors in ore centration areas and the relationships between the structure of crust and upper mantle at depth and the deep metallogenic process are illustrated. According to the global examples, the detection results of deep seismic reflection profile provide deep clues for the formation of large ore concentrated areas. The reflective transparent zone may be the upward migration channel of the mantle fluid, forming the mineral and energy sources of ore concentration area, indicating that the mantle material is involved in mineralization. Fracture systems characterized by strong reflectivity, including large-scale faults, detachments and crustal shear zones, are pathways through which metallogenic fluids migrate upward from the lower crust. The"bright spot"in the deep seismic reflection profiles of ore concentrated areas may be the reflection of the residual magma chamber formed after the deep magma of volcanic activity surges into the middle crust. Revealing the deep fine structure not only plays an important role in the reconstruction of the tectonic historical evolution of ore concentration area, but also has crucial guiding significance for the determination of the future metallogenic potential and the target area of the foreground.
Electrical Structure of Narusongduo Ore Concentration District and Its Constraints on Mineralization
2019, 44(6): 2106-2116.
doi: 10.3799/dqkx.2019.030
Abstract:
To understand the electrical structure in Narusongduo ore concentration district in the Tibetan Plateau and its constraints on mineralization, the magnetotellurics data in the district were carefully processed and analyzed, obtaining a reliable 2-D electrical model. The study shows that there are some conductors at depths of about 40-50 km, 20-30 km and 10 km, which may be resulted from the partial melting and aqueous fluids. As the deposits in the district belong to the magmatic-hydrothermal type, and the upwelling deep-seated magma played an important role in the mineralization, the crustal conductors may offer constraints to the ore-related magma reservoirs, and connecting these conductors also may represent the ancient ascending channels. The electrical structure indicates the relationship between the crustal conductors and the regional metallogenic dynamics in our study. The ascending ore-bearing magma also may migrate to the Pb-Zn and Fe-Cu locations by the local hidden structures, and subsequently evolved into the ore body.
To understand the electrical structure in Narusongduo ore concentration district in the Tibetan Plateau and its constraints on mineralization, the magnetotellurics data in the district were carefully processed and analyzed, obtaining a reliable 2-D electrical model. The study shows that there are some conductors at depths of about 40-50 km, 20-30 km and 10 km, which may be resulted from the partial melting and aqueous fluids. As the deposits in the district belong to the magmatic-hydrothermal type, and the upwelling deep-seated magma played an important role in the mineralization, the crustal conductors may offer constraints to the ore-related magma reservoirs, and connecting these conductors also may represent the ancient ascending channels. The electrical structure indicates the relationship between the crustal conductors and the regional metallogenic dynamics in our study. The ascending ore-bearing magma also may migrate to the Pb-Zn and Fe-Cu locations by the local hidden structures, and subsequently evolved into the ore body.
2019, 44(6): 2117-2128.
doi: 10.3799/dqkx.2018.352
Abstract:
The Zhaxikang ore-concentration area (ZOCA) is the most abundant polymetallic ore enrichment area discovered recently in the South Tibet. However, the geophysical work carried out in the ore -concentrated areas is not sufficient due to the limited working conditions, and the deep structure and geological information are not clear, which seriously restricts the understanding of its mineralization and potential of the ore-concentrated areas and other important geological problems. In order to find out the deep geological structure and to discuss the deep mechanism of mineralization, measurements of gravity, magnetic and magnetotelluric were carried out in Zhaxikang area. By using gravity and magnetic anomalies due to two-dimensional wavelet decomposition, density and electrical structure model, and analyses of petrophysical and geological properties, it is indicated that there were 3-layers in geophysics of the Cuonadong gneiss dome. In addition, lower unit (core) mainly consisted of leucogranite, which extends north into the deep of the Zhaxikang Pb-Zn polymetallic deposit. The leucogranite combined with N-S normal faultsystem and other secondary faults made up the ore -forming system of the Zhaxikang overprinting and remobilization ore deposit. The Cuonadong gneiss dome was located in high and low zones of electrical blocks, with formation mechanism likely related with the South Tibet Detachment System (STDS). On the other hand, deep extension of Cuonadong rock and emplacement of leucogranite drove fluid circulation, and the Zhaxikang deposit was formed in combination with influence of other factors.
The Zhaxikang ore-concentration area (ZOCA) is the most abundant polymetallic ore enrichment area discovered recently in the South Tibet. However, the geophysical work carried out in the ore -concentrated areas is not sufficient due to the limited working conditions, and the deep structure and geological information are not clear, which seriously restricts the understanding of its mineralization and potential of the ore-concentrated areas and other important geological problems. In order to find out the deep geological structure and to discuss the deep mechanism of mineralization, measurements of gravity, magnetic and magnetotelluric were carried out in Zhaxikang area. By using gravity and magnetic anomalies due to two-dimensional wavelet decomposition, density and electrical structure model, and analyses of petrophysical and geological properties, it is indicated that there were 3-layers in geophysics of the Cuonadong gneiss dome. In addition, lower unit (core) mainly consisted of leucogranite, which extends north into the deep of the Zhaxikang Pb-Zn polymetallic deposit. The leucogranite combined with N-S normal faultsystem and other secondary faults made up the ore -forming system of the Zhaxikang overprinting and remobilization ore deposit. The Cuonadong gneiss dome was located in high and low zones of electrical blocks, with formation mechanism likely related with the South Tibet Detachment System (STDS). On the other hand, deep extension of Cuonadong rock and emplacement of leucogranite drove fluid circulation, and the Zhaxikang deposit was formed in combination with influence of other factors.
2019, 44(6): 2129-2142.
doi: 10.3799/dqkx.2018.362
Abstract:
A crustal scale extension occurred in the post-collisional stage of the Tibetan Plateau, and tectonic-thermal events closely related to stretching, such as leucogranites, north-south and east-west faults, were developed in the Tethyan Himalayan and developed series of Pb-Zn-Sb-Au polymetallic deposits. The Zhaxikang Pb-Zn-Sb-Au polymetallic deposit is the only superlarge polymetallic deposit in the belt. This paper applies a multi-scale integrated geophysical method to Zhaxikang's prospecting prediction and can provide reference for the exploration of deposits in the Tethys Himalayan Pb-Zn-Sb-Au metallogenic belt. Firstly, the spatial relationship of tectonic-thermal events was initially established by the north-south MT section (72 km long and 1 km from the reference point) crossing the Cuonadong dome and the South Tibet detachment system (STDS). Combined with the time relationship of regional tectonic-thermal events, a possible tectonic-thermal coupling mineralization was proposed, which provides a basis for the geophysical exploration of Zhaxikang. Secondly, through the joint interpretation of 400 km2, 1:50 000 regional gravity (line distance 500 m, dot distance 400 m) and MT(dot distance 400 m) shallow information, the fault system of the Zhaxiang assembly area was established. Finally, the Zhaxikang polymetallic ore body was delineated by the joint interpretation of the 9 km2 IP measurement (line distance 100 m, dot distance 40 m) and the AMT profile(dot distance 50 m) and gravity(dot distance 20 m).
A crustal scale extension occurred in the post-collisional stage of the Tibetan Plateau, and tectonic-thermal events closely related to stretching, such as leucogranites, north-south and east-west faults, were developed in the Tethyan Himalayan and developed series of Pb-Zn-Sb-Au polymetallic deposits. The Zhaxikang Pb-Zn-Sb-Au polymetallic deposit is the only superlarge polymetallic deposit in the belt. This paper applies a multi-scale integrated geophysical method to Zhaxikang's prospecting prediction and can provide reference for the exploration of deposits in the Tethys Himalayan Pb-Zn-Sb-Au metallogenic belt. Firstly, the spatial relationship of tectonic-thermal events was initially established by the north-south MT section (72 km long and 1 km from the reference point) crossing the Cuonadong dome and the South Tibet detachment system (STDS). Combined with the time relationship of regional tectonic-thermal events, a possible tectonic-thermal coupling mineralization was proposed, which provides a basis for the geophysical exploration of Zhaxikang. Secondly, through the joint interpretation of 400 km2, 1:50 000 regional gravity (line distance 500 m, dot distance 400 m) and MT(dot distance 400 m) shallow information, the fault system of the Zhaxiang assembly area was established. Finally, the Zhaxikang polymetallic ore body was delineated by the joint interpretation of the 9 km2 IP measurement (line distance 100 m, dot distance 40 m) and the AMT profile(dot distance 50 m) and gravity(dot distance 20 m).
2019, 44(6): 2143-2154.
doi: 10.3799/dqkx.2018.373
Abstract:
In order to reveal the alteration and mineralization structure of the Gangjiang porphyry copper-molybdenum deposit, the short-wave infrared spectroscopy (SWIR) technique was systematically used to analyze the four drill-holes in the typical section of the deposit.Five types of altered mineral groups were detected, i.e.sericite, kaolinite, chlorite, sulphate and carbonate.Short wave infrared spectroscopy results of sericite show that there is a greater illite crystallinity (≥ 1.5) and a smaller sericite Al-OH absorption position (≤ 2 205 nm) towards the ore body.However, the value of illite crystallinity and sericite Al-OH absorption position distal the ore body are 0.8-1.2 and 2 207-2 209 nm, respectively.In addition, the iron oxide intensity value is synchronized oxidized ore body.It is indicated that these characteristic parameters of short-wave infrared spectroscopy are helpful to the understanding of the alteration and mineralization structure of the Gangjiang porphyry Cu-Mo deposit, which may effectively restrict the ore-forming fluid condition and provide a potential prospecting indicator for the target mine and other similar mining areas.
In order to reveal the alteration and mineralization structure of the Gangjiang porphyry copper-molybdenum deposit, the short-wave infrared spectroscopy (SWIR) technique was systematically used to analyze the four drill-holes in the typical section of the deposit.Five types of altered mineral groups were detected, i.e.sericite, kaolinite, chlorite, sulphate and carbonate.Short wave infrared spectroscopy results of sericite show that there is a greater illite crystallinity (≥ 1.5) and a smaller sericite Al-OH absorption position (≤ 2 205 nm) towards the ore body.However, the value of illite crystallinity and sericite Al-OH absorption position distal the ore body are 0.8-1.2 and 2 207-2 209 nm, respectively.In addition, the iron oxide intensity value is synchronized oxidized ore body.It is indicated that these characteristic parameters of short-wave infrared spectroscopy are helpful to the understanding of the alteration and mineralization structure of the Gangjiang porphyry Cu-Mo deposit, which may effectively restrict the ore-forming fluid condition and provide a potential prospecting indicator for the target mine and other similar mining areas.
2019, 44(6): 2155-2186.
doi: 10.3799/dqkx.2019.105
Abstract:
The orogenic gold deposits show features as follows:relation to oceanic plate subduction and terrane accretion, hosted by metamorphic massif along convergent plate boundaries, controlled by ductile to brittle shear zones, low salinity and H2O-CO2-CH4 dominating ore fluid, wide formation depths varying from about 2 to 20 km and formation temperatures ranging within 200-650℃, temperature-dependent alteration and ore mineral assemblages. Orogenic gold deposits formed coevally to the time of cycled convergences of supercontinents. Due to the diversity of wall rock types and ore-controlling structures, ambiguity of ore geochemistry, uncertainty of fluid and metal sources and their evolutions, and disparity between source regions and ore deposition locations, two distinct origin models were proposed for orogenic gold deposits. The first is metamorphic fluid model, in which the deposits formed in prograde metamorphism of orogeny with different source from evolving regional upper crust. The auriferous fluid is considered to release from greenschist-to amphibolite-facies prograde metamorphism of upper crustal rocks, during which gold and other metals are liberated from transformation of pyrite to pyrrhotite. This model was universally applied to Phanerozoic orogenic gold deposit shosted by greenschist-facies terranes. However, it was recognized that most orogenic gold deposits formed in retrogression stage subsequent to peak metamorphism or without any spatial-temporal link to regional metamorphism, which challenged the metamorphic fluid model. Thus the mantle fluid model, which indicates that ore fluids for orogenic gold deposits are derived from devolatilization of subducted oceanic plate or fertile mantle, was proposed. Although the mantle fluid model is not compatible with the petrological diagram in phase equilibrium condition, the extensive proofs for the existence of mantle fluids and their appearance near surface support that mantle fluids are capable to transport to upper crustal levels under supercritical conditions and phase unequilibrium. The Chinese orogenic gold deposits are divided into seven gold belts:Silurian belt along Jiangnan orogen, Permian belt in Tianshan and Altay orogen, Triassic to Jurassic one along northern margin of North China craton (Solonker orogen), Triassic to Jurassic one within Paleo-Tethyan orogens, Jurassic one along southern margin of South China block possibly controlled by the Paleo-Tethyan closure, Cretaceous one along southern margins of North China craton, and Paleogene one in Tibetan Plateau and its margins. Orogenic gold deposits in China formed in Phanerozoic in association with various orogeny, with ore-forming ages post dating peak metamorphism. Case studies on gold districts in these belts, such as Jiaodong, Ailaoshan, and western margin of Yangtze craton, all favored the mantle fluid model.
The orogenic gold deposits show features as follows:relation to oceanic plate subduction and terrane accretion, hosted by metamorphic massif along convergent plate boundaries, controlled by ductile to brittle shear zones, low salinity and H2O-CO2-CH4 dominating ore fluid, wide formation depths varying from about 2 to 20 km and formation temperatures ranging within 200-650℃, temperature-dependent alteration and ore mineral assemblages. Orogenic gold deposits formed coevally to the time of cycled convergences of supercontinents. Due to the diversity of wall rock types and ore-controlling structures, ambiguity of ore geochemistry, uncertainty of fluid and metal sources and their evolutions, and disparity between source regions and ore deposition locations, two distinct origin models were proposed for orogenic gold deposits. The first is metamorphic fluid model, in which the deposits formed in prograde metamorphism of orogeny with different source from evolving regional upper crust. The auriferous fluid is considered to release from greenschist-to amphibolite-facies prograde metamorphism of upper crustal rocks, during which gold and other metals are liberated from transformation of pyrite to pyrrhotite. This model was universally applied to Phanerozoic orogenic gold deposit shosted by greenschist-facies terranes. However, it was recognized that most orogenic gold deposits formed in retrogression stage subsequent to peak metamorphism or without any spatial-temporal link to regional metamorphism, which challenged the metamorphic fluid model. Thus the mantle fluid model, which indicates that ore fluids for orogenic gold deposits are derived from devolatilization of subducted oceanic plate or fertile mantle, was proposed. Although the mantle fluid model is not compatible with the petrological diagram in phase equilibrium condition, the extensive proofs for the existence of mantle fluids and their appearance near surface support that mantle fluids are capable to transport to upper crustal levels under supercritical conditions and phase unequilibrium. The Chinese orogenic gold deposits are divided into seven gold belts:Silurian belt along Jiangnan orogen, Permian belt in Tianshan and Altay orogen, Triassic to Jurassic one along northern margin of North China craton (Solonker orogen), Triassic to Jurassic one within Paleo-Tethyan orogens, Jurassic one along southern margin of South China block possibly controlled by the Paleo-Tethyan closure, Cretaceous one along southern margins of North China craton, and Paleogene one in Tibetan Plateau and its margins. Orogenic gold deposits in China formed in Phanerozoic in association with various orogeny, with ore-forming ages post dating peak metamorphism. Case studies on gold districts in these belts, such as Jiaodong, Ailaoshan, and western margin of Yangtze craton, all favored the mantle fluid model.
2019, 44(6): 2187-2196.
doi: 10.3799/dqkx.2019.115
Abstract:
The Urumieh-Dokhtar magmatic arc (UDMA), hosting three giant and six large Miocene porphyry copper deposits, is the most important post collisional porphyry belt in the Tethyan domain. In the UDMA belt, there are also abundant coeval barren porphyry intrusions, but the factors controlling fertility of Miocene porphyry intrusions in the belt remains enigmatic. The Dalli deposit, located in the central segment of UDMA, contains both fertile and barren Miocene intrusions. In this study, we report zircon petrography, geochronology, trace element geochemistry and Hf isotopic compositions for the barren diorite and mineralization-related quartz diorite porphyry at Dalli. The results show that the diorite has inherited zircon cores overgrown by new zircons, whereas quartz diorite only has one type of zircon. The diorite yields a zircon U -Pb age of 17.4±0.3 Ma, which is slightly older than the quartz diorite porphyry (zircon U-Pb:15.6±0.1 Ma), and the inherited zircon cores yielded as zircon U-Pb of 172-920 Ma. Both the diorite and quartz diorite porphyry show slightly positive εHf(t) values, which are respectively +2-+4 and +2-+5.Miocene zircons from both diorite and quartz diorite porphyry are characterized by obviously positive Ce anomalies and slightly depleted Eu anomalies. However, the inherited zircon cores exhibit more depleted Eu anomalies, suggesting low oxygen fugacity. These results suggest that the barren diorite possibly interacted with ancient crust, particularly with reduced material, which subsequently decreased magma oxygen fugacity whereas the fertile quartz diorite porphyry emplaced without such material exchange. On the basis of above observations, we propose magma process may be the first order of key factors controlling the fertility of intrusions in the central segment of the UDMA.
The Urumieh-Dokhtar magmatic arc (UDMA), hosting three giant and six large Miocene porphyry copper deposits, is the most important post collisional porphyry belt in the Tethyan domain. In the UDMA belt, there are also abundant coeval barren porphyry intrusions, but the factors controlling fertility of Miocene porphyry intrusions in the belt remains enigmatic. The Dalli deposit, located in the central segment of UDMA, contains both fertile and barren Miocene intrusions. In this study, we report zircon petrography, geochronology, trace element geochemistry and Hf isotopic compositions for the barren diorite and mineralization-related quartz diorite porphyry at Dalli. The results show that the diorite has inherited zircon cores overgrown by new zircons, whereas quartz diorite only has one type of zircon. The diorite yields a zircon U -Pb age of 17.4±0.3 Ma, which is slightly older than the quartz diorite porphyry (zircon U-Pb:15.6±0.1 Ma), and the inherited zircon cores yielded as zircon U-Pb of 172-920 Ma. Both the diorite and quartz diorite porphyry show slightly positive εHf(t) values, which are respectively +2-+4 and +2-+5.Miocene zircons from both diorite and quartz diorite porphyry are characterized by obviously positive Ce anomalies and slightly depleted Eu anomalies. However, the inherited zircon cores exhibit more depleted Eu anomalies, suggesting low oxygen fugacity. These results suggest that the barren diorite possibly interacted with ancient crust, particularly with reduced material, which subsequently decreased magma oxygen fugacity whereas the fertile quartz diorite porphyry emplaced without such material exchange. On the basis of above observations, we propose magma process may be the first order of key factors controlling the fertility of intrusions in the central segment of the UDMA.
