卡林型金矿床的特征和成因

卡林型金矿床主要分布在北美大盆地地区科迪勒拉造山带、科罗拉多地台和我国扬子地块西南缘的板内古生代 -中生代沉降带和西北缘古生代 -中生代冒地槽。具有分布局限、成矿集中的特点 ,形成许多超大型矿床。金矿床成矿域发育一套大面积分布的巨厚的古 -中生代冒地槽建造 ,同成矿期的岩浆活动和构造活动强烈 ,有利于形成各种地热体系和流体活动。金矿床往往形成成矿带 ,单个金矿床的规模大小不一 ,矿化受构造、围岩和深部流体控制 ,围岩一般具有还原性质。围岩蚀变为去碳酸盐化、硅化、泥化、硫化物化和重晶石化等。金与砷黄铁矿、黄铁矿及毒砂紧密相关 ,以次显微金的形式存在。其他矿物为雄黄、雌黄、重晶石、辉锑矿、石英、方解石、含铊矿物以及表生矿物明矾石和黄钾铁矾等。成矿流体中水为大气降水 ,碳、硫主要来源于矿床围岩和以下岩石 ,少量可能来源于深部。矿床形成于浅 -中等深度。提出了大气降水热液、岩浆热液、变质热液和卤水成矿等卡林型金矿床形成模式 ,大气降水成因模式能较好解释金矿床的地质地球化学特征。

CHARACTERISTICS AND ORIGIN OF THE CARLIN-TYPE GOLD DEPOSITS

The Carlin-type gold deposits are mostly found in the Cordillera orogen and Colorado platform, Great basin region of North America and Paleozoic-Mesozoic intra-block depressed zone at the southwest margin of the Yangtze block and miogeosyncline northwest of the Yangtze block. This type of gold deposits occurs locally, as many superlarge ore deposits. In the minerogenetic regions of this type of gold deposits, very thick and widely distributed Paleozoic-Mesozoic miogeosyncline sediments are developed; tectonic movements and magmatic activities were developed extensively at the same time, favoring ore-formation and the formation of geothermal systems and the cycling of hydrothermal fluids. The Carlin-type gold deposits often constitute minerogenetic zones and have reserves of different scales. The mineralization is controlled by structures, strata and deep fluids and is commonly associated with deoxidized wallrocks. The wallrock alteration includes de-carbonization, silicification, clay grouting, sulfidization and baritization. Gold is submicroscopic and associated with arsenic pyrite, pyrite and arsenopyrite tightly. Other minerals in the ore are realgar, opiment, barite, stibnite, quartz, calcite, Tl-bearing minerals and hypergene minerals, alunite and pastreite. It is shown that water in the ore-forming hydrothermal fluid is meteoric; carbon and sulfur come mostly from wallrock and rocks beneath the deposits, though a little comes from the deep. The mineralization occurred at shallow to middle depth. Models of ore-formation by meteoric, magmatic, metamorphic and brine hydrothermal fluids respectively have been put forward. The mineralization model of meteoric hydrothermal fluid is able to reasonably explain the geological and geochemical characteristics of the Carlin-type gold deposits.