福建紫金山矿床硫砷铜矿的成因研究

A Study on genesis of enargite from Zijinshan Copper Deposit,Fujian Province,China

福建紫金山铜矿是我国高硫化型浅成低温热液矿床研究的热点之一。本文针对该矿床中普遍发育的硫砷铜矿进行了仔细的矿相观察及电子探针化学成分分析,对其成因进行了初步研究。该矿床中硫化物矿物之间存在着一定的交代、穿插以及化学组分的继承关系。矿物生长遵循黄铁矿-硫砷铜矿-斜方蓝辉铜矿、蓝辉铜矿-铜蓝的交代生长顺序。结合室内水热反应模拟实验结果,推测矿床经历了2期、4阶段热液事件:第1期第1阶段形成黄铁矿;第2阶段形成硫砷铜矿;第2期第1阶段形成各种铜硫化物,铜蓝在第2期第2阶段形成。其中硫砷铜矿中的砷元素来自于岩浆热液,其显示出交代先成黄铁矿的特征,也有少量结晶于矿石的较大裂缝处形成自形柱状晶体。表生带中的硫化物矿物曝露在地表或潜水中遭受风化剥蚀,逐渐形成高硫型浅成热液,并沿构造裂隙持续下渗至岩体附近受热折返,在下渗和折返的过程中交代先成的黄铁矿和硫砷铜矿,生成斜方蓝辉铜矿和蓝辉铜矿等铜硫化物,该交代反应符合'耦合的溶解再沉淀'的成因机制。热液下渗和受热折返是1个循环往复的过程。

Zijinshan copper deposit is one of the hottest spots of high sulfidation epithermal deposits in China,this paper focus on the study of enargite from Zijinshan to reveal its genesis by means of optical microscope and EPMA composition analysis. Results show some definite relationships of replacement reaction, interpenetration and component inheritance among copper sulfides,and establish a genesis sequence of pyrite-enargite-anilite and digenitecovellite. Two phases of hydrothermal alteration can be deducted as it combines with the results of hydrothermal experiments; pyrite and enargite formed in the first phase,other copper sulfides and covellite formed in the second phase. Arsenic carried by magmatic hydrothermal fluid formed enargite by both replace reaction and precipitation.Most of enargites show characteristics of replacing pyrite,and there are also a few enargites formed euhedral columnar crystals in fractures. Minerals in the upper oxidation zone suffered by weathering denudation formed high sulfidation meteoric solution,and infiltrated downward through fractures. It was heating during its downward infiltrating process,and finally returned to the top as it reached the hot igneous rock. Through this process pyrite and enargite took precedence being replaced. This phase transformations occurred between deep minerals and the high sulfidation epithermal achieved by dissolution and reprecipitation,and the solutions formed a circling of infiltration and heating process.