西藏多龙矿集区荣那铜金矿床蚀变矿物学和地球化学及找矿意义

Alteration mineralogical and geochemical features of the Rongna deposit in Duolong mining district of Tibet and their deep prospecting significances

位于西藏多龙矿集区的荣那铜金矿床是班公湖-怒江成矿带首例斑岩型-浅成低温热液型矿床,它的发现对于班公湖-怒江成矿带找矿模型的构建以及资源潜力评估有着重要意义。本文以荣那矿床ZK3204岩芯钻孔为研究对象,针对其蚀变矿物,运用短波红外光谱测试技术,并结合金属矿物组合以及黄铁矿LA-ICP-MS原位微量元素特征,以期查明其矿床成因,并为深部资源勘查提供理论依据。短波红外光谱测试显示出ZK3204钻孔蚀变矿物垂向分带组合为:高岭石+(地开石)→高岭石+伊利石→高岭石+(地开石+石膏)→高岭石+绢云母+伊利石→高岭石+伊利石+(叶腊石)+(地开石),金属矿物也从Cu-S体系逐渐转变为Cu-Fe-S体系。通过黄铁矿LA-ICP-MS原位微量元素分析发现,黄铁矿可分为四类,分别对应荣那矿床四个成矿阶段:(1) Py I:Co、Ni、Cu、Ag、Au含量较低,Co/Ni显示为沉积成因,代表成岩期黄铁矿;(2) PyⅡ:Co、Ni含量较低,Cu、Ag、Au含量较高,Co/Ni显示为沉积成因,代表第一期斑岩型矿床成矿期黄铁矿;(3) PyⅢ:Co含量较低,Ni、Cu、Ag、Au含量较高,Co/Ni显示为沉积成因,代表第二期斑岩型矿床成矿期黄铁矿;(4) PyⅣ:Cu、Ag、Au含量较低,Co、Ni含量较高,Co/Ni显示为热液成因,代表浅成低温热液矿床成矿期黄铁矿。风化作用也是荣那矿床重要地质过程,贯穿于各成矿阶段,反映为早白垩世班公湖-怒江洋盆向北俯冲消减大背景下的多龙矿集区隆升事件,导致矿床被大量剥蚀,也使黄铁矿显示沉积成因。荣那矿床目前仍有较大找矿潜力,在钻孔深部(815m以下),黄铁矿Cu、Ag、Au含量,钻孔中Cu、Pb、Zn、Cr、Hg等含量,绢云母、伊利石含量以及铜金矿的矿石品位均有向下升高的趋势,说明在ZK3204钻孔下部仍有巨大的找矿潜力,可作为未来深部资源探测的重点对象。

The Rongna Cu-Au deposit,located within the Duolong mining district,is the first discovered epithermal porphyry deposit in the Bangong-Nujiang metallogenic belt,and it is of great importance to built the prospecting model and to assess the resource potential along this belt. The alteration assemblages and ore minerals and pyrite’s LA-ICP-MS trace element features of ZK3204 drilling are studied to determine the genesis of deposit,and to provide theoretical foundation for deep resource exploration in this area. It is found that alteration minerals identified by shortwave infrared techniques exhibits vertical zoning of kaolinite +( dickite) →kaolinite +illite→kaolinite +( dickite + gypsum) →kaolinite + sericite + illite→kaolinite + illite +( pyrophyllite) +( dickite),and Cu-S systematic metallic minerals gradually become Cu-Fe-S systematic metallic minerals. The LA-ICP-MS trace element analyses of these pyrites demonstrates four mineralization stages in the Rongna deposit,which are corresponding to four types of pyrites,respectively,namely:( 1) Py I,regarded as the product of diagenetic stage,containing low value of Co,Ni,Cu,Ag,Au,and Co/Ni is interpreted as sedimentary in origin;( 2) Py Ⅱ,regarded as the product of porphyry deposit stage I,containing low value of Co,Ni,and rich in Cu,Ag,Au,and Co/Ni is interpreted as sedimentary in origin;( 3) Py Ⅲ,regarded as the product of porphyry deposit stage Ⅱ,containing low value of Co,and rich in Ni,Cu,Ag,Au,and Co/Ni is interpreted as sedimentary in origin;and( 4) Py Ⅳ,regarded as the product of epithermal deposit stage,containing low value of Cu,Ag,Au,and rich in Co,Ni,and Co/Ni is referred to be the result of hydrothermal activities. Weathering is also an important geological process in the Rongna mineralization stages,which is leaded by the uplifting of the Duolong mining district area generated by northward subduction of the Bangong-Nujiang oceanic crust at Early Cretaceous,eroding some part of ore body,and making pyrites shown as sedimentary ones in origin. The Rongna deposit also shows great resource potential and prospecting under the bottom of drilling( below 815 m) since contents of Cu,Pb,Zn in pyrites,and contents of Cu,Pb,Zn,Cr,Hg,sericite and illite of the drilling cores all have trends to extend to the under part,showing there is still a large prospecting potential of porphyry deposit under ZK3204 drilling,which could be an important target for deep resource exploration in the future.