甘肃李坝金矿围岩蚀变与金成矿关系

Wall Rock Alteration and Its Relations to Gold Mineralization of the Liba Gold Deposit,Gansu Province

西秦岭地区是目前国内造山型和卡林型金矿找矿的热点地区之一,已发现的甘肃李坝造山型金矿为超大型规模。以李坝金矿6号矿带为例,系统地研究了其蚀变矿物组合、近矿围岩蚀变分带及相应的金矿化特征,总结了矿床(带)的蚀变分带模式。该模式具典型的中心式环带结构,可分为3个蚀变带,由中心向外依次为黄铁绢英岩化带、绢云母化带和绿泥石化带。蚀变矿物组合分别为黄铁矿+绢云母+石英±毒砂±白云母±电气石±方解石、绢云母+绿泥石+石英+黄铁矿±黑云母及绿泥石+黑云母±绢云母±黄铁矿;与这3个蚀变带相对应的是金的富集带、矿化带和无矿带。蚀变岩石物质组分迁移分析表明,围岩蚀变及其分带是热水流体/岩石反应时岩石化学组分发生迁移的结果,矿化伴随着蚀变发生,且金矿化与黄铁矿化和浸染状硅化关系最为密切。

Western Qinling orogenic belt is one of the hot spots for orogenic and Carlin-type gold deposits exploration in China, where a super large gold deposit called Liba has been found. After choosing the No. 6 ore belt of Liba gold deposit as a case for systemically studying alteration mineral association, host rock alteration zoning and gold mineralization features, the authors sum up the alteration zoning mode of this type of gold deposit. Typical concentric zonal structure can be distinguished clearly, which shows that three alteration zones from inner to outer are pyritization silicification-sericitization zone, sericitization zone and chloritization zone. The altered mineral assemblages in each zone are pyrite ＋ sericite ＋ quartz ± arsenopyrite ± muscovite ± tourmalinite ± calcite, serieite ＋ chlorite ＋ quartz ＋ pyrite ± biotite and chlorite ＋ biotite ± sericite ± pyrite respectively, and corresponding to the three alteration zones which are Au enrichment zone, Au mineralization zone and no Au mineralization zone. Migration of elements in alteration rock shows that alterations of wall rock and its zoning are resulted by hydrothermal fluid and rock reaction; Au mineralization occurs accompanied with mineral alteration, and mineralization of Au has a close relation to pyrite mineralization and disseminated silicatization.