墨江金矿床的成矿物质来源探讨

DISCUSSION ON METALLOGENIC MATERIAL SOURCE OF MOJIANG GOLD DEPOSIT

以往,对墨江金矿床的成矿物质来源存在着三种不同的看法(观点):(1)成矿物质来源于金厂组(下-中志留统)浅变质岩系;(2)成矿物质来源于距今2700Ma的古老基底;(3)成矿物质主要来源于金厂蚀变超基性岩体。本文从矿床的同位素组成、微量元素、包体成分等方面,论证墨江金矿床的成矿物质主要来源于金厂蚀变超基性岩体,金厂组变质岩系也可能提供少量的成矿物质。矿床属于浅成中-低温热液成因。含矿热液是有大量大气降水加入的Ca^(++)+Mg^(++)/SO_4型流体。超基性岩体滑石化、蛇纹石化、碳酸盐化过程中,在碱性、相对还原的介质条件下,金等成矿物质主要以硫络合物的方式进入成矿溶液,并在fO_2、fS_2、pH,Eh、T、P等物理化学参数发生变化的条件下沉淀。

In the past, there were three different views on metallogenic material source of Mojiang gold deposit: (1)metallogenic materials originate from epimetamorphic rock system of Jinchang Formation(Lower-Middle Silurian); (2)metallogenic materials originate from palaeobasement of 2700 Ma;(3) metal-logenic materials mainly originate from Jinchang altered ultrabasic rockbody. In respects of isotopic compositions, trace elements and inclusion compositions of the deposit, this paper proves that the metallogenic materials of the gold deposit mainly originate from Jinchang altered ultrabasic rockbody, and that the metamorphic rock system of Jinchang Formation could provide a few metal-logenic materials. The genesis of the deposit belongs to shallow-seated meso-thermal-epithermal. Ore-bearing solution is Ca^2+Mg^2+/S_4~2-type fluid mixed with large quan-tity of atmospheric water. During the process of talcization, serpentinization and carbonation of the ultrabasic rockbody, the gold and other metallogenic materials join metallogenic solution as sulfur complex under the conditions of alkalis and relative reduction, and deposit under the conditions of the changes of physical and chemical parameters, such as fO2, fS_2, pH, Eh, T, P, etc.