云南白牛厂银多金属矿床喷流沉积成因证据:容矿岩石的地球化学约束

The Exhalative-sedimentary Evidence of the Bainiuchang Ag-polymetallic Deposit,Yunnan,China:Constraints from Geochemistry of Host-rocks

滇东南是否存在广泛的热水沉积活动已成为制约滇东南三大多金属矿床(个旧、都龙、白牛厂)成因研究的主要因素之一。系统研究了白牛厂银多金属矿床容矿岩石的地球化学特征,研究表明:矿床容矿岩石主量元素数据均投影于火山及海底热卤水成因区域内;稀土元素明显分为两组,稀土元素总量较高的样品可能与较多的正常沉积物的加入有关;稀土元素总量较低的样品具有与加拿大沙利文矿山的条带状富电气石热液沉积岩和加拿大Agnico-Eugle矿山的铁建造中的条带状燧石岩相似的稀土元素配分模式与标准化参数;同时,微量元素对的演化趋势与现代大洋热水沉积物相似,而且As、Sb和Ag含量与大厂和个旧热水沉积硅质岩相当。推测白牛厂银多金属矿床属热水沉积成矿,只是在距花岗岩体较近的部位遭受了部分叠加改造。

Studying if there took place extensive exhalative-sedimentary activities in the southeast Yunnan Province has been one of key factors to constrain origin of the Gejiu,Bainiuchang,and Dulong polymetallic deposits.The authors systematically study the geochemistry characteristics of host-rocks in the Bainiuchang Ag-polymetallic deposit in this paper.The host-rocks have the same distribution area with the sea-floor volcano or hot-water origin chert.Then normalized REE distribution patterns of host-rocks can be divided into two groups： One group with higher total REE contents indicates more normal sediments attendance.The other group with lower total REE contents possesses the similar normalized REE distribution patterns and parameters with rich-tourmaline banded hydrothermal sediments in the Canada Sullivan deposit and banded chert in iron-bearing formations in the Canada Agnico-Eugle deposit.And the pairs of trace elements show the similar characteristics with modern sea-floor hydrothermal sediments.In addition,the contents of As,Sb and Ag are similar with that of chert in the Dachang and the Gejiu mining districts.Based on above of all,it is indicated that the Bainiuchang Ag-polymetallic deposit is exhalative-sedimentary origin.