Intracontinental orogenic structure-altered lithofacies mapping and prospecting model of the Changgou gold deposit in the Hanyin gold orefield, South Qinling
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摘要:
大比例尺矿田构造-蚀变岩相填图技术是矿田构造物理化学研究和整装勘查区综合研究中逐渐形成的一项新技术。通过对南秦岭石泉-旬阳金矿整装勘查区调研和大比例尺矿田构造填图示范，认为在矿田尺度实施1：25000构造-岩相填编图、在矿区尺度实施1：10000或1：5000构造-蚀变岩相填编图是可行有效的。南秦岭汉阴北部金矿田近十年来经过矿田构造-蚀变岩相填图和专题研究，找矿预测进展较大。其中，长沟金矿是近年矿田构造-蚀变岩相填图找矿和整装勘查区综合研究新发现的、受脆-韧性剪切带控制的蚀变岩型金矿床。长沟金矿床位于脆-韧性剪切带DSZ3(RF5)内。含矿岩性主要是下志留统梅子垭组糜棱岩化含黑云母变斑晶绢云母石英片岩和含石榴子石绢云母石英片岩。与成矿密切相关的蚀变主要有黑云母化、硅化、黄铁矿化、绢云母化。当黑云母变斑晶发育、石英脉密集发育，伴有黄铁矿化，且离构造破碎带80~150 m时，金矿化品位较高。成矿流体主要属中-低温、中-低盐度、低密度的NaCl-H2O-CO2体系，成矿压力为41.03~98.04 MPa，成矿深度为1.52~3.63 km。与成矿有关的花岗闪长岩脉和花岗细晶岩锆石LA-ICP-MS年龄为180.2±3.6~176.0±1.9 Ma。长沟矿区黑云母变斑晶化蚀变岩金矿石中黑云母40Ar-39Ar年龄为178.44±0.81 Ma，反等时线年龄为178.20±0.76 Ma。明确了该矿区蚀变岩成岩和金成矿时代为早侏罗世，成矿时代属于燕山期陆内。
Abstract:The large-scale tectonic altered lithofacies mapping technology is a new technology gradually formed in the study of the tectonics-physics-chemistry of the orefield and the comprehensive study of the whole survey area. Based on the survey of the Shiquan-Xunyang gold mineraliztion belt in the South Qinling Mountain and the large-scale orefield structure mapping demonstration, it is considered that the 1:25000 tectonic-lithographic mapping implemented at the orefield scale and 1:10000 or 1:5000 structure-altered lithofacies mapping implemented at the mining area scale are feasible and effective. In the past ten years, the gold orefield in the north of Hanyin County, South Qinling, has made great progress in ore prospecting by structure-altered lithofacies mapping and special studies. The Changgou gold deposit in Hanyin County is a new type of altered rock type gold deposit controlled by brittle-ductile shear zones, which was discovered during comprehensive research on ore structure-altered rock facies mapping in recent years. The Changgou gold deposit is located in the DSZ3 brittle-ductile shear zone (RF5), where the lithology is mainly mylonitized biotite-bearing phenocryst sericite quartz schist and garnet bearing sericite quartz schist of Lower Silurian. The alterations of the rock closely related to mineralization are biotitization, silicification, pyrite mineralization, and sericitization. Where biotite morphology is developed and quartz veins are developed densely accompanied by pyrite mineralization and is about 80~150 meters away from the later stage main fracture belt, the gold mineralization grade is relatively high. The ore-forming fluid mainly belongs to the medium-low temperature, medium-low salinity, and low-density NaCl-H2O-CO2 system. The ore-forming pressure is from 41.03 MPa to 98.04 MPa and the ore-forming depth is from 1.52 km to 3.63 km. The granodiorite veins and granite aplite related to mineralization measured by U-Pb zircon LA-ICP-MS have ages from 180.2±3.6 Ma to 176.0±1.9 Ma. The 40Ar-39Ar age of biotite is 178.44±0.81 Ma, and the reverse isochron age is 178.20±0.76 Ma. It is obvious that the ore-forming epoch of altered rock and gold is early Jurassic, and the ore-forming age belongs to Yanshanian intracontinental orogeny in this orefield. Ore-controlling structures and metallogenic structural planes belong to the brittle-ductile shear zone and its fracture system. On the basis of this study, a prediction model of the intracontinental orogenic hydrothermal altered rock type gold deposit in the Changgou gold mining area was established, and it is inferred that the extensional shear fold superimposed altered rock on the left and the periphery of the northwest of the mining area seems to be a rich ore block. In addition, the prospecting direction in the deep area is pointed out.
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致谢: 十分感谢中国地质科学院地质力学研究所吕古贤研究员对矿田构造和蚀变岩相填图指导帮助，感谢陕西省地质调查院王北颖、陕西地矿西安地质矿产勘查开发院有限公司杨志学、陕西地矿第一地质队有限公司赵新科、吴邦朝、邓德平等教授级高工对野外调研工作的大力支持，感谢有色金属矿产地质调查中心方维萱研究员的细致评审和宝贵修改意见。
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图 1 汉阴北部金矿田1:25000构造-岩相图与脆-韧性剪切带DSZ分布①
Figure 1. 1:25000 structural lithofacies map and distribution of brittle-ductile shear zone in northern Hanyin gold orefield
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图 2 长沟金矿区1:10000构造-蚀变岩相图②
Figure 2. 1:10000 structure-altered lithofacies map of the Changgou gold ore district
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图 3 汉阴北部长沟金矿区受脆-韧性剪切带DSZ3控制的构造-蚀变岩类型
Figure 3. Structure-altered rock types controlled by the brittle-ductile shear zone DSZ3 in the Changgou gold ore district in northern Hanyin
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图 4 长沟金矿区28勘探线控矿构造-蚀变与花岗闪长岩脉分布图
1—变石英砂岩；2—绢云母石英片岩；3—含黑云母变斑晶绢云石英片岩；4—含炭黑云母变斑晶绢云石英片岩；5—含石榴子石绢云石英片岩；6—断层破碎带；7—花岗闪长岩脉；8—石英脉；9—黄铁矿化；10—矿体；11—S2面理产状(倾向/倾角)；12—脆-韧性剪切带编号；13—钻孔编号
Figure 4. Ore control structure alteration and granodiorite vein distribution along No. 28 exploration line of the Changgou gold ore district
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图 5 长沟金矿区新生矿物和石英细脉顺S2面理定向发育特征素描(a)和照片(b、c)
Q—石英；Bi—黑云母；S1—第一期面理；S2—第二期面理；a—左图为早期S1面理和石英团块被S2面理切穿，中图为沿S2面理分布的石英脉和团块，右图为沿S1和S2面理分布的斑晶状黑云母；b—顺S2面理产出的石英脉；c—黑云母变斑晶石英(细粒化和糜棱岩化)云母糜棱片岩显微照片，10×4(+)
Figure 5. Orientation development of new minerals and quartz veinlet along S2 foliation in the Changgou gold ore district
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图 6 汉阴北部金矿田长沟-鹿鸣金矿床找矿预测模型
Figure 6. Prospecting prediction model of the Changgou-Luming gold deposit, in the northern Hanying gold orefield
表 1 长沟金矿区“三位一体”找矿预测地质模型
Table 1 Geological model of "trinity" prospecting in the Changgou Changgou gold ore district
成矿地质体 主体归属大型变形构造，以燕山期(侏罗纪)陆内造山期脆-韧性剪切带DSZ大型变形构造为主，叠加有岩浆期后热液和热变质带、断裂破碎带、煌斑岩脉、花岗闪长岩脉等 成矿构造及成矿结构面 成矿构造 晚印支期—燕山期陆内造山期逆冲推覆-滑脱-走滑复合构造岩片带，脆-韧性剪切带DSZ、多期构造叠加带、断裂破碎蚀变带、岩浆期后热液叠加和热变质带 成矿结构面 变质细砂岩与云母石英片岩界面+物理化学转换界面+次生成矿结构面，主要为新生面理+多期构造置换S2面理+面理产状突变带+软硬岩性界面+断裂破碎带 结构类型 二元结构：大型脆-韧性剪切带DSZ+S2面理+断裂破碎带与中低温岩浆期后热液叠加控矿模式 成矿作用特征标志 梅子垭组-斑鸠关组变砂岩与片岩界面、变硅质岩与变泥质粉砂岩界面、含碳层段磁黄铁矿化、磁黄铁矿化、褐铁矿化等。脆-韧性剪切变形带、石英细脉、石英团块等密集发育段，黑云母变斑晶+石榴石变斑晶叠加发育段，复杂紧闭的揉皱变形带、拔丝状黄铁矿发育段、断层破碎矿化蚀变带、S2面理弯曲突变地段、岩浆期后热液和热变质叠加段 
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