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    沉积岩容矿层状铜矿床中首次发现金矿物:以滇中某铜矿为例

    The firstly-discovered gold minerals in sediment-hosted stratiform copper (SSC) deposits: a case study in central Yunnan province, China

    • 摘要: 扬子陆块西南缘康滇铜铁成矿省是我国重要的铜铁资源基地,主要发育海相火山岩型铁氧化物铜金矿床(简称IOCG矿床)和沉积岩容矿层状铜矿床(简称SSC矿床)。长期以来,该成矿省金矿化多被认为主要与IOCG矿床有关,而对SSC矿床中发育的金矿化现象鲜有报道。文章以滇中某SSC矿床为例,通过详细的矿物学研究,首次在该类矿床中发现了金矿物,并将其鉴定为银金矿。金矿物呈晶隙金或包体金充填于斑铜矿、辉砷钴矿等矿物裂隙或晶界中。矿石原岩中的Au品位较低(未检出),部分Ag品位达25.4 g/t,铜精粉中的Au品位为0.18~0.22 g/t,Ag品位为38~42 g/t。电子探针元素面扫描结果显示,金矿物中Au与Ag分布特征高度吻合,证实金以Ag-Au合金的形式出现。Au-Ag的元素空间分布与Cu、Co、As、S的元素空间分布不完全重叠,进一步证明Au-Ag合金为独立的金矿物,而非以固溶体的形式赋存于载金硫化物中。结合矿相学观测结果,认为金主要以独立矿物相形式存在,并与Co-As元素具有空间相关性,其成矿特征与典型IOCG矿床中的金不同。此外,本次发现某SSC矿床中的金矿物可能由后期富金流体充填早期形成的斑铜矿和辉砷钴矿裂隙或晶界形成。研究区SSC矿床中金矿物的首次发现,不仅提升了对研究区SSC矿床成因的理解,也为滇中乃至整个康滇地区共/伴生金矿勘查提供了新的找矿方向。

       

      Abstract: As an important Cu-Fe resource base in China, the Kangdian Cu-Fe metallogenic province on the southwestern edge of the Yangtze Block mainly developed marine volcanic rocks-hosted iron oxide-copper-gold deposits (IOCG) and sediment-hosted stratiform copper deposits (SSC). For a long time, it is considered by many that gold mineralization in this province is related to IOCG deposits, while there have been few reports on the development of gold mineralization in SSC deposits. This work took a SSC deposit in central Yunnan as an example, through in-depth and detailed mineralogical research, discovered gold mineral, such as electrum, for the first time in this type of deposit. It occurs as interstitial gold or inclusion gold in mineral fractures or grain boundaries such as bornite and cobaltite. The gold grade in the original ores is relatively low and undetectable, with individual silver grade of 25.4 g/t. The Au and Ag grades in the copper concentrate powder range from 0.18 to 0.22 g/t and 38 to 42 g/t, respectively. The electron probe elemental surface mapping results show that the distribution of Au and Ag in the gold mineral is highly consistent, confirming that gold appears in the form of Ag-Au alloy. The spatial distribution of Au-Ag elements does not completely overlap with the spatial distribution of Cu, Co, As and S elements, further proving that Au-Ag alloy is an independent gold mineral, rather than a simple solid solution existing in gold bearing sulfides. Based on mineralogical observations, this study suggests that gold mainly exists in the form of independent mineral phases and has spatial correlation with Co-As elements. Its mineralization characteristics are different from those of gold in typical IOCG deposits. In addition, it is highly likely that the gold in the SSC deposit was formed by later gold-rich fluids filling and encapsulating early formed bornite and cobaltite. The first discovery of gold minerals in the SSC deposits in the research area not only enhances the understanding on the genesis of SSC deposits, but also provides a new direction for gold exploration in central Yunnan and even the entire Kangdian region.

       

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