推荐回答(1个)
(1)金矿床空间分布具有区域性集中的明显趋势。我国各省区均有金矿床产出,但各省区的金储量却判若霄壤,大部分黄金储量分布于滨太平洋成矿域中,其次为古亚洲成矿域和特提斯-喜马拉雅成矿域。受成矿背景的制约,在各成矿域中的金矿床分布也极不均衡,大多数金矿床产于古地台区及其边缘坳陷或断陷带中,如胶东金矿集中区拥有我国已探明金储量的30%,黑龙江沿江地区集中了我国大部分的砂金储量,长江中下游是我国最重要的伴生金产区,其伴生金储量占该带总储量的74%。
(2)大型金矿床较少,中小型金矿床居多。至1992年,在已探明的1057个金矿产地中,大型矿床占4.7%,中型占20.5%,小型占74.8%。近年来,我国金矿床地质勘查工作得到飞速发展,加之对金矿床成矿理论、成矿模型、成矿系列认识的深化,大型矿床的比例有增加的趋势。至1993年6月,在被统计的346个岩金矿床中,大型矿床66个,其储量占61%,其中有30个是近期发现或储量大幅度增长的大型矿床(潘辉逖,1994)。可以预料,随着地质工作的不断深入,大、中型矿床的比例将有所增加。但是与国外富金国家相比,我国金矿床规模普遍偏小。据不完全统计,国外金储量大于1000t者7个,500~1000t的12个,100~500t的59个,而我国单个金矿床储量绝大多数均在100t以下,这与国外黄金储量绝大部分集中在少数超大型矿床中的情况不同。E.M.涅克拉索夫(1980)报道了国外“深延”矿床的情况,矿化深度很大,平均深达1600m,最深可达3500m(印度科拉尔金矿床),而我国金矿体延深多在千米以内。
(3)伴生金矿床在我国具有重要意义,其探明储量约占我国金储量的30%以上,而其保有储量约为32%,说明伴生金矿床的利用率较低。应该指出,我国许多伴生金矿床均属于大型矿床之列,如江西德兴铜厂铜矿田中的伴生金达二百余吨,是我国金矿床储量之最,但是这部分金只能伴随主元素开采,形成“细水长流”之势。
(4)成矿作用多次叠加,即有原生作用又有转生作用,赋矿岩系与金矿床的形成存在时差,是我国金成矿的重要特色。我国地壳经历了多期次的构造变动。岩浆活动和热液作用,促成了金的多次富集,特别是东部在中生代卷入了滨太平洋构造域,发生了大规模的构造、岩浆活动,形成了一批与燕山期构造-岩浆作用有关的岩浆期后热液成矿作用和前寒武纪变质基底中的叠加成矿作用,胶东、冀东、小秦岭、辽北-吉南、内蒙古、两广、陕西等地方均发现金矿床的再生富集现象,燕山期热事件在我国金成矿中占有举足轻重的地位。在原生和转生含金岩系基础上,与重熔岩浆作用有关的金矿床类型是我国金矿床殊于世界金矿床的重要特色。
(5)在不同大地构造单元,金成矿带有其特征的矿化类型和成矿特点。不同大地构造单元所处的深部构造位置、基底与盖层建造、构造变动、岩浆活动、变质作用及所经历的热历史不同,促成金的矿化类型、控矿因素、成矿作用的宏观和微观标志存在重要差别。如产于太古宇绿岩建造中的金矿床主要产于华北地台,具有多期成矿特征,其早期与区域变质有关,晚期常具有显生宙岩浆热液叠加成矿的特点。元古宙含金浅变质岩系常分布于地台隆起的边缘裂陷区,形成被褶皱构造控制的层状、鞍状矿体及受韧性剪切带制约的蚀变岩型金矿化。该类金矿床广布于我国辽、吉、冀、蒙、豫、鄂、湘、赣、川、陕、晋、粤、桂、琼诸省区,是我国重要金矿化类型和找矿远景区。古生代-三叠纪含金沉积岩系中微细浸染型金矿床以滇、桂、黔三角区最为发育,属华南加里东褶皱系右江褶皱带,区内岩浆岩不发育,矿化产于古生界-三叠系粉砂岩、碳酸盐岩及泥硅质岩系中,是我国重要的找矿远景区。显生宙含金火山岩系中的金矿床主要出现在古火山机构的边缘,分布于我国西部的古生代次火山岩系中及我国东部中-新生代火山岩区,特别集中于火山断陷的边缘区。
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