投稿时间：2021-01-22
修订日期：2021-10-28
网络发布日期：2022-01-11
中文摘要:关键金属锡作为全球高科技产业的重要战略性资源,其成矿作用及找矿勘查均是目前国际矿床学领域研究的热点。位于滇东南有色金属成矿带西端的个旧具有全球规模最大的锡矿储量,因其具有独特的成矿条件而备受关注。近年来,在个旧老厂矿田西部凹陷带花岗岩体内部发现中型-大型铜-锡多金属矿体,但对其尚缺乏系统的研究。文章对个旧老厂矿田重点坑道和钻孔开展构造-岩相蚀变特征解析,观察到锡铜矿化主要以石英-电气石-萤石-硫化物-锡石脉的形式产于似斑状蚀变花岗岩中,少量以萤石硫化物形式产于花岗岩与碳酸盐接触带的矽卡岩中。文章对与2种成矿作用相关的萤石开展LA-ICP-MS及ICP-MS微量元素和Sr-Nd同位素分析。结果显示:蚀变花岗岩型脉状萤石∑REE为(7~749)×10-6(LA-ICP-MS)、(45.5~77.4)×10-6(ICP-MS),具有强烈的Eu负异常(δEu=0.01~0.08)和弱Ce负异常(δCe=0.56~0.92),(87Sr/86Sr)i变化于0.709 53~0.711 47;矽卡岩型萤石∑REE为(27.2~1277.0)×10-6(LA-ICP-MS)、(29.8~161.0)×10-6(ICP-MS),具有显著的Eu负异常(δEu=0.01~0.19)和弱的Ce负异常(δCe=0.44~1.05),(87Sr/86Sr)i变化于0.708 70~0.715 53。通过综合分析这2类萤石的地球化学特征,认为蚀变花岗岩型脉状萤石与矽卡岩型萤石均形成于氧化向还原过渡的环境,且均为岩浆热液活动的产物。2类萤石为近同期形成,其中矽卡岩型萤石中Ca来源于老卡等粒花岗岩和碳酸盐岩地层,蚀变花岗岩型萤石中Ca主要来源于老卡等粒花岗岩。综上,个旧老厂矿田西部凹陷带的似斑状花岗岩为老卡等粒花岗岩体边部的早阶段岩体,其未提供成矿物质,但提供了流体运移通道和就位空间,晚阶段流体上升侵位在老厂西部凹陷带似斑状花岗岩体内部形成岩浆热液脉型铜-锡多金属矿体。该研究可以为个旧锡矿深部及外围增储和滇东南锡矿带下一步找矿方向提供重要的理论指导。
Abstract:Tin,as an important strategic resource for the global high-tech industry,is a hot topic for international research in the field of ore deposit metallogeny and prospecting.The Gejiu Sn deposit,located at the western end of the non-ferrous metallogenic belt in southeastern Yunnan,has the largest Sn reserves in the world.The deposit has attracted much attention because of its unique mineralization conditions.In recent years,medium to largescale Cu-Sn polymetallic ore bodies have been found within the granite in the western depressional zone of the Laochang ore field in Gejiu.However,there is a lack of systematic studies on these ore bodies.Based on the analysis of structural and lithofacies alteration features in key tunnels and drill holes,we observed that Cu-Sn mineralization occurs mainly as quartz-tourmaline-fluorite-sulfide-cassiterite veins wthin the altered porphyritic granites,or as fluorite-sulfides within the skarn in the contact zone between granite and carbonate rocks,and the LA-ICP-MS,ICP-MS trace element and Sr-Nd isotopic analysis of fluorites associated with two kinds of mineralization were carried out.The results show that the altered granite type fluorite vein has ∑REE values varying from 7×10-6 to 749×10-6(LA-ICP-MS),and from 45.5×10-6 to 77.4×10-6(ICP-MS);it shows strong negative Eu anomalies (δEu=0.01~0.08) and weak negative Ce anomalies (δCe=0.56~0.92),(87Sr/86Sr)i varies from 0.709 53 to 0.711 47. Skarn type fluorite has∑REE values of 27.2×10-6 to 1277×10-6(LA-ICP-MS) and 29.8×10-6 to 161×10-6(ICP-MS),significant negative Eu anomaly (δEu=0.01~0.19) and weak negative Ce anomaly (δCe=0.44~1.05),the (87Sr/86Sr)i varies from 0.708 70 to 0.715 53.A comprehensive analysis suggests that both altered granite type vein fluorite and skarn type fluorite were formed in transitional environment from oxidation to reduction,and are the products of magmatic hydrothermal activity.The two types of fluorites were formed almost contemporaneously,and the Ca of the skarn-type fluorite is derived from the Laoka equal-grained granite and carbonate strata,but the Ca of the altered granite type fluorite is mainly derived from the Laoka equal-grained granite.In summary,the porphyritic granite in the western depressional zone of the Laochang ore field is an early-stage marginal body of the Laoka equal-grained granite,which provided fluid transport channels and emplacement space.When the late stage fluid ascending and emplacing along the fault,the Cu-Sn polymetallic ore bodies formed inside the porphyritic granite in the western depressional zone of the Laochang.This study can provide important theoretical guidance for increasing reserves in deep and peripheral areas of Gejiu and the next step prospecting direction of Sn ore belt in southeastern Yunnan.
keywords:geology Cu-Sn polymetallic deposit altered granite type fluorite trace elements Sr-Nd isotope Gejiu
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基金项目:国家自然基金面上项目(编号:41673060)、云锡校企合作项目(编号:GF-2018-01、GF-2021-01)联合资助
引用文本：
彭强,江小均,李超,范柱国,魏超,陈耀坤,谢小明,禹华.2021.云南个旧西凹蚀变花岗岩型铜-锡多金属矿床萤石地球化学特征及其地质意义[J].矿床地质,40(6):1182~1198PENG Qiang,JIANG Xiao-jun,LI Chao,FAN Zhu-guo,WEI Chao,CHEN Yao-kun,XIE Xiao-ming,YU Hua.2021.Geochemical characteristics of fluorites from the Xi'ao altered granite type Cu-Sn polymetallic deposit in Gejiu, Yunnan Province and their geological significance[J].Mineral Deposits40(6):1182~1198
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