中国岩浆铜镍钴硫化物矿床成矿理论创新和找矿突破

Study of ore-forming theoretical innovation and prospecting breakthrough of magmatic copper-nickel-cobalt sulfide deposits in China

中国岩浆铜镍钴硫化物矿床是国家镍、钴、铂族元素等战略性关键金属资源的主要来源,是需要特别关注的具有未来价值的重要矿床类型。该类矿床来源于上地幔,特别是软流圈的部分熔融形成的镁铁质、超镁铁质岩浆,硫化物液相-硅酸盐熔体的不混溶(熔离)作用是成矿的主要机制。它们主要形成于两种背景:大陆裂谷和造山带中的伸展环境。中国是岩浆铜镍钴硫化物矿床的产出大国,但与国外相比,形成背景和成矿动力学机制比较独特。世界上绝大多数岩浆铜镍钴硫化物矿床都形成于古老的克拉通,是地幔柱地球动力作用的结果,太古代—早元古代的科马提岩镍钴硫化物矿床是鲜明的产出特点。中国缺少古老的科马提岩有关的镍钴硫化物矿床,成矿时代相对较晚,主要形成于新元古代、晚古生代早期和晚期三个时期,新元古代以镍金属资源量居世界第三的金川超大型矿床为代表,晚古生代早期以近年来找矿突破发现的夏日哈木超大型矿床为代表。夏日哈木矿床也是迄今世界上特提斯造山带中发现的唯一一例超大型岩浆铜镍钴硫化物矿床。中国学者基于中国找矿实际提出的“大岩浆-深部熔离-贯入”表现为“小岩体成大矿”的成矿理论,广泛为野外地质勘查工作者接受并应用,取得了重要的找矿突破性成果,同时为国外同行认可,改变了岩浆铜镍钴硫化物矿床传统的成矿认识。造山带中岩浆铜镍钴硫化物矿床的广泛分布是中国该类矿床的一个重要特色,按形成造山带演化和成矿历史的不同,可分为特提斯型和中亚型两种重要的类型。特提斯型以夏日哈木矿床为代表,它是特提斯构造转换,原特提斯造山后,古特提斯裂解的产物;中亚型以中亚造山带中东天山-北山、阿尔泰分布的大批晚古生代晚期早二叠世岩浆铜镍钴硫化物矿床为代表,是板块构造和地幔柱双重地球动力学机制作用的结果。中国岩浆铜镍钴硫化物矿床找矿潜力巨大,金川矿床作为水平的“岩床”被推覆至地表呈倾斜的“岩墙”产出的结果,深边部仍具有重要找矿潜力,目前已在含矿岩体两端发现了重要的新矿体;夏日哈木矿床所在的东昆仑及其邻区已发现十余处新的矿床(点)。区域上,塔里木陆块东南缘、塔里木陆块北缘、扬子陆块西缘和华北陆块东北缘是亟待加强勘查的找矿远景区,而扬子陆块北缘、华北陆块北缘是急需调查的找矿新区。

Chinese magmatic copper-nickel-cobalt sulfide deposit is the main source of strategic key metal resources,such as nickel,cobalt and platinum group elements in China,and it is an important deposit type with a future value that needs special attention.This type of deposit comes from the mafic and ultramafic magma formed by the upper mantle,especially the asthenosphere,and the immiscible(liquation)action between sulfide liquid-silicate melt is the main mineralization mechanism.They are mainly formed in two geological settings:the continental rift and the extended environment in the orogenic zone.China is a major producer of magmatic copper-nickel-cobalt sulfide deposits,but compared with the world it is relatively unique.Most magmatic copper-nickel-cobalt sulfide deposits in the world are formed in the ancient craton,and are the result of the mantle plume geodynamics.Archeozoic-early Proterozoic komatiite nickel-cobalt sulfide deposits is a distinct metallogenic characteristics.Ancient komatiite-related nickel-cobalt sulfide deposits have been rarely discovered in China,and their mineralization age is relatively late,mainly in the Neoproterozoic,Early and Late Paleozoic.The Neoproterozoic is represented by the Jinchuan super-large deposit with nickel metal reserves ranked the third in the world,and the Early Paleozoic by the Xiarihamu super-large deposit discovered in the prospecting breakthrough of recent years.The Xiarihamu deposit is also the only super-large magmatic copper-nickel-cobalt sulfide deposit found in the Tethys orogenic belt in the world.Mineralization theory of“big magma-deep immiscibility-injection”and“forming big ore deposits in small intrusive rocks”proposed by Chinese scholars based on China’s prospecting practice has been widely accepted and applied by field geological exploration workers,and has made important prospecting breakthrough discoveries.At the same time,it has been recognized by foreign peers,which changed the traditional metallogenic understanding of magma copper-nickel-cobalt sulfide deposits.The extensive distribution of magmatic copper-nickel-cobalt sulfide deposits in orogenic belts is an important feature of such deposits in China.According to the different evolution of orogenic zones and metallogenic history,it can be divided into two important types:Tethys type and Central Asian type.The Tethys type is represented by the Xiarihamu ore deposit,and it is the product of the Tethys structural transformation,which the Paleo-Tethys cracking after the Proto-Tethys orogeny;the Central Asian type is represented by a large number of the early Permian of the Late Palaeozoic magmatic copper-nickel-cobalt sulfide deposits distributed in the Eastern Tianshan-Beishan and Altai zones of the Central Asian Orogenic belt,which is the result of the dual geodynamics mechanism of plate tectonics and mantle plume.China’s magmatic copper-nickel-cobalt sulfide deposit has huge prospecting potential,and the Jinchuan deposit as a result of nappe structure from deep horizontal“sill”thrusted to the surface of the inclined“dyke”,it still has significant prospecting potential in its deep and marginal locations,in which important new ore bodies have been found at both ends of the ore-bearing rock body;more than 10 new ore deposits(points)have been found in East Kunlun and its adjacent areas,where the Xiarihamu deposit is located.In the region,the southeastern margin of Tarim Landmass,the northern margin of Tarim Landmass,the western margin of Yangtze Landmass and the northeast margin of North China Landmass are the exploration prospect areas to strengthen prospecting,while the northern margins of Yangzi Landmass and North China land block are the new prospecting areas for urgent investigation.