Metallogenic Characteristics and Metallogenic Model of the Pegmatite Type Uranium Deposit in Danfeng Area, Eastern Qinling Mountains
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摘要: 伟晶岩型铀矿是北秦岭成矿带东段重要的铀矿类型，本文介绍了该类型铀矿的矿体特征、矿石特征、副矿物特征和年代学特征.铀矿体产于淡色含榴花岗岩体内外接触带伟晶岩脉中，围绕花岗岩体产出，形态复杂，随伟晶岩脉的形态而变化，呈似脉状、透镜状和不规则状，晶质铀矿为最主要的工业矿物.通过LA-ICP-MS锆石U-Pb定年获得含铀伟晶岩年龄为404.3±1.4 Ma，略晚于淡色含榴花岗岩体年龄，矿岩时差小，显示了岩浆成矿的特征.综合分析表明早泥盆世丹凤地区进入后碰撞构造环境，秦岭岩群发生部分熔融形成富铝含榴花岗质岩浆，随着岩浆结晶分异演化的不断进行，铀元素以U4+形式与O2-结合形成晶质铀矿，在岩体内外接触带黑云母富集部位沉淀成矿.三叠纪后接受长期隆升剥蚀，侵入岩呈岩株出露地表，围绕岩株外带产出的含铀伟晶岩脉，表现为光石沟式铀矿床.随着隆升剥蚀作用的进一步加剧，侵入岩顶部相遭受剥蚀之后以岩基出露地表，在岩体的内接触带不规则形态的含铀伟晶岩出露地表，表现为陈家庄式铀矿床.依据成矿模式，预测伟晶岩型铀矿成矿远景区2片，分别为大毛沟地区和纸房沟地区.Abstract: Pegmatite-type uranium deposit is the most important uranium deposit in the eastern part of northern Qinling metallogenic belt. This paper presents a study of the metallogenic and geochronological characteristics of the ore body,ores,and accessory minerals. Uranium ore-body occurs in pegmatite dykes around the garnet-bearing leucogranite and uraninite is the major industry mineral. The accessory minerals of uranium bearing pegmatite are similar to those of garnet-bearing granitic rocks,but different from gneissic granitic rocks. The results of LA-ICP-MS zircon U-Pb dating of uranium bearing pegmatite is 404.3±1.4 Ma,Early-Devonian. Comprehensive data suggest that the Danfeng garnet-bearing granitic rocks were derived from partial melting of Qinling Group in the post-collision setting during Early-Devonian. The residue magmas were enriched in Th-U and other moderate-incompatible elements but low content of volatile component which have relative short migration. The pegmatite-type uranium was formed near the internal and external contact zone of the pluton. The pluton was emplaced as the stock in the surface which experienced the long time uplift and erosion after the Triassic. Then the uranium-bearing pegmatite dykes were distributed around the stock,which resulted in the Guangshigou uranium deposit. The intrusions at the top were emplaced as the batholiths in the surface after the anabatic uplift and erosion. Thus,the uranium-bearing pegmatites were developed in the internal contact zone,for example,Chenjiazhuang uranium deposit. Based on the metallogenic model,Damaogou and Zhifanggou areas are determined as two areas of metallogenic prospect of pegmatite-type uranium deposit.
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图 1 东秦岭丹凤地区伟晶岩脉密集区分布示意
图 1a据Lai et al.(2008)修改；图 1b据孙圭和赵致和(1998)修改
Fig. 1. Geological sketch of pegmatite Danfeng area, East Qinling
图 2 丹凤地区伟晶岩岩石学特征
a.内带岩瘤状伟晶岩；b.外带岩脉状伟晶岩；c.侵入接触关系；d.黑云母伟晶岩
Fig. 2. The petrology characteristics of granitic pegmatites of Danfeng area
图 3 陈家庄矿床13号(a)和光石沟铀矿床0号(b)勘探线剖面
Fig. 3. Cross sections of No. 13 exploration line in Chenjiazhuang deposit and No. 0 exploration line in Guangshigou deposit
图 4 陈家庄矿床伟晶岩中晶质铀矿二次电子图像
Q.石英；Ab.钠长石；Ur.晶质铀矿；Py.黄铁矿；Zr.锆石
Fig. 4. Secondary electron image showing uraninite in pegmatite of Chenjiazhuang deposit
图 5 岩屋沟黑云母花岗伟晶岩典型锆石CL图像和U-Pb年龄协和图
Fig. 5. Zircon CL images and U-Pb concordia diagram of biotite pegmatite, Yanwugou area
图 6 丹凤地区伟晶岩型铀矿成矿模式
Fig. 6. Uranium metallogenic model of pegmatite type uranium deposit, Danfeng area
表 1 丹凤地区内带和外带含铀伟晶岩特征对比
Table 1. Geological characteristics of the inner and outer uranium bearing pegmatite in Danfeng area
伟晶岩类型 内带伟晶岩 外带伟晶岩 相同 岩石类型 黑云母伟晶岩 铀矿物 晶质铀矿 年龄 416~404 Ma 差异 围岩 淡色含榴花岗岩 片麻岩 接触关系 渐变过渡接触 侵入接触 结构 粗粒-伟晶结构 伟晶结构 形态 复杂：囊状、团块状、不规则状 简单：脉状 规模 小：几十米，大者数百米 大：最大可达3 km以上 矿化特征 连续性差，不稳定 连续性好，矿化延伸稳定 
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表 2 晶质铀矿在矿石中的产出部位分布(%)
Table 2. The distribution (%) of uraninite in different formed position of ore-body
产出部位 Pl Q Mi Bi Grt Ap Bi-Ms 总计 矿物中 6 7 13 12 1 / 1 17 边缘 11 14 13 76 / 1 / 49 粒间 80 34 注：Pl.斜长石；Q.石英；Mi.微斜长石；Bi.黑云母；Grt.石榴子石；Ap.磷灰石；Bi-Ms.黑云母白云母化.
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表 3 含铀黑云母伟晶岩副矿物含量(10-6)
Table 3. Accessory minerals of bearing uranium Bt-pegmatite(10-6)
样品编号 Grt Mnz Zr Ap Py Lm Ilm Mo Fl Ur Au 采样位置 91-29 7 554 543 316 9 少量 / / 少量 / 57 / 桑树坪 91-3 少量 117 450 26 / 13 1 022 11 少量 588 / 华银坪 91-12 15 67 134 少量 / 61 / / / 21 / 王佛堂 91-11 少量 29 少量 323 12 205 28 / / 68 / 王佛堂 91-20 少量 17 20 47 < 1 / / < 1 / 1 664 / 狮子坪 91-23 39 258 86 < 1 1 / 378 < 1 / 547 / 骑马河 90-13 少量 8 微量 / 微量 / / 微量 / 5 753 / 小花岔 91-34 3 856 16 少量 840 / / / / 8 031 / 小花岔 91-8 152 326 65 / 少量 / / / / 356 / 李家湾 90-28 微量 1 627 微量 / 1 117 / / 微量 / 1 600 0.023 光石沟 90-16 21 905 微量 95 / 24 / / 微量 / 143 0.011 李家湾 90-24 23 363 微量 23 / 297 / / / / 283 0.049 大东沟 注：Grt.石榴石；Mnz.独居石；Zr.锆石；Ap.磷灰石；Py.黄铁矿；Lm.褐铁矿；Ilm.钛铁矿；Mo.辉钼矿；Fl.萤石；Ur.晶质铀矿；Au.自然金；据孙圭和赵致和(1998).
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表 4 丹凤地区花岗岩、伟晶岩主要副矿物对比(10-6)
Table 4. Accessory minerals of pegmatite and granite of Danfeng area(10-6)
岩性矿物 Mag Ttn Aln Mnz Zr Ap Ur Grt 片麻状花岗岩 1 883 56.6 63.0 4.7 17.7 739 1.8 / 1 938 28.8 32.4 / 3.0 176 / / 淡色含榴花岗岩 1 396 51.5 少量 39 3.9 155 少量 2.9 黑云母伟晶岩 少量 少量 少量 438 107 14.8 2 421 102 28.8 少量 少量 1 627 微量 少量 1 600 153 注：Mag.磁铁矿；Ttn.榍石；Aln.褐帘石；Mnz.独居石；Zr.锆石；Ap.磷灰石；Ur.晶质铀矿；Grt.石榴石；据孙圭和赵致和(1998).
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表 5 丹凤地区含铀黑云母伟晶岩LA-ICP-MS锆石U-Pb测年数据
Table 5. LA-ICP-MS zircon U-Pb age dates of Bi-Pegmatite of Danfeng area
测点 同位素含量(10-6) Th/U 同位素比值 同位素年龄(Ma) Total Pb 232Th 238U 207Pb/ 206Pb 1σ 207Pb/ 235U 1σ 206Pb/ 238U 1σ 207Pb/ 206Pb 1σ 207Pb/ 235U 1σ 206Pb/ 238U 1σ D4850-01 249 135 6 031 0.02 0.061 8 0.000 8 0.553 6 0.010 3 0.064 9 0.000 6 733 28 447 7 405 3 D4850-02 276 65 6 661 0.01 0.061 3 0.000 3 0.548 0 0.005 8 0.064 8 0.000 3 650 11 444 4 405 2 D4850-03 203 51 5 253 0.01 0.058 0 0.000 4 0.518 7 0.005 3 0.065 0 0.000 4 528 10 424 4 406 2 D4850-04 239 90 6 177 0.01 0.059 1 0.000 4 0.536 3 0.013 6 0.065 6 0.001 3 569 17 436 9 409 8 D4850-05 259 60 6 856 0.01 0.057 0 0.000 3 0.506 9 0.005 3 0.064 6 0.000 3 500 11 416 4 403 2 D4850-06 292 171 7 442 0.02 0.058 3 0.000 9 0.507 1 0.009 1 0.063 2 0.000 5 543 33 417 6 395 3 D4850-07 248 199 6 323 0.03 0.055 1 0.000 3 0.496 1 0.006 5 0.065 4 0.000 5 417 19 409 4 408 3 D4850-08 245 162 6 184 0.03 0.058 2 0.000 4 0.517 2 0.006 6 0.064 4 0.000 4 600 15 423 4 403 2 D4850-09 177 173 4 695 0.04 0.056 5 0.000 3 0.507 6 0.005 1 0.065 1 0.000 3 472 11 417 3 406 2 D4850-10 500 554 11 396 0.05 0.060 0 0.000 5 0.528 4 0.009 1 0.063 9 0.001 0 606 17 431 6 399 6 D4850-11 185 29 5 045 0.01 0.055 6 0.000 4 0.498 7 0.005 6 0.065 0 0.000 4 435 15 411 4 406 2 D4850-12 246 149 6 179 0.02 0.059 6 0.000 5 0.538 1 0.007 3 0.065 3 0.000 4 587 19 437 5 408 2 D4850-13 225 118 6 151 0.02 0.055 2 0.000 3 0.493 9 0.005 2 0.064 7 0.000 4 420 11 408 4 404 2 D4850-14 239 158 6 333 0.03 0.057 0 0.000 3 0.507 5 0.005 1 0.064 5 0.000 4 500 11 417 3 403 2 D4850-15 233 471 6 067 0.08 0.055 9 0.000 3 0.499 9 0.005 1 0.064 7 0.000 2 456 11 412 3 404 1 D4850-16 308 44 7 920 0.01 0.058 4 0.000 3 0.521 6 0.007 3 0.064 4 0.000 3 546 -23 426 5 403 2
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