亚洲中部及邻区成矿元素的演化趋势

The evolutionary tendency of ore-forming elements in Central Asia and adjacent areas

亚洲中部及邻区的成矿作用,在地球演化早期即前寒武纪,以碳、硼、磷、镁、金、铁、铜等为主,在晚期即显生宙后期,以铝、铅锌、钨锡、钼、汞锑等为主。前寒武纪碳(C,石墨矿)的集中发育可能与地球早期地壳和大气圈中氧丰度不高有关,碳不易氧化;硼(B)、磷(P)说明在地球演化早期,地壳中相对富含挥发分元素;镁(Mg)、铁(Fe)、金(Au)说明在地球演化早期,地壳中镁铁质成分占据主导地位。铜(Cu)系多期成矿的元素,其成矿作用主要发生在元古宙、古生代和中生代。在经济上有意义的铝(Al)即铝土矿的成矿高峰期,以中国为例,主要出现在石炭—二叠纪。铅(Pb)、锌(Zn)、钨(W)、锡(Sn)、钼(Mo)主要成矿于中生代。汞(Hg)、锑(Sb)初步沉积在古生代,但成矿则主要在中生代,一般说来,比铅、锌、钨、锡、钼更晚。这些元素在周期表中的位置,C、B、P、Mg、Al属第2～3周期,其成矿主要出现在地球演化早期;Fe、Au、Cu、Pb、Zn、W、Sn、Mo、Hg、Sb属第4～6周期,其成矿主要出现在地球演化晚期。铀(U)为第7周期,成矿更晚;中国铀矿的成矿主要在钨(W)、锡(Sn)、钼(Mo)、铋(Bi)、铁(Fe)、铜(Cu)、锌(Zn)、铌(Nb)、钽(Ta)、稀土(REE)等所有矿化之后。换言之,在地球的演化历史中,成矿元素的原子结构由简单逐渐趋于复杂,其外层电子层数由2～3层(C,B,P等)发展到多达7层(U)。由此可见,在普查找矿中,寻找周期表前部的元素的矿床,应当主要在古老地壳地区(前寒武纪地层发育地区)进行;寻找周期表中部的元素的矿床,在古老地壳地区和年青地壳地区都应注意;而寻找周期表后部的元素的矿床,则主要应在年青地壳发育地区,即年青的地质、构造、岩浆及热液活动发育的地区进行。显生宙以来,特别是晚古生代和中生代以来,地球上水圈、大气圈和生物圈的进一步发育,使成矿元素的演化趋势进一步复杂化;这一阶段外生矿床主要是沉积矿床的形成,以及特别是碳、氢和氧的再循环,导致了大量煤、石油和天然气的生成。

Mineralizations in Central Asia and adjacent areas were dominated by C,B,P,Mg,Au,Fe and Cu in the early stage（in Precambrian） of evolution of the earth,and by Al,Pb,Zn,W,Sn,Mo,Hg and Sb in the late stage（in late Phaneozoic）.Carbon（graphite） dominated in Precambrian might have been related to the low oxygen fugacity in the crust and the atmosphere in the early stage of the earth;in that case carbon was not easy to be oxidized.B and P are volatile elements,hence their enrichment in Precambrian may imply that the crust was relatively enriched with B and P in the early stage of the earth.Mg,Fe and Au compositions indicate that the crust was rich in these elements at that time.Cu mineralization took place repeatedly in Proterozoic,Paleozoic and Mesozoic.Economically important Al deposits,i.e.,bauxite deposits,presented peak mineralization in Carboniferous and Permian,as can be seen in China.Pb,Zn,W,Sn,Mo deposits were formed in Mesozoic.Hg and Sb,though primarily deposited in Paleozoic,were mainly formed in Mesozoic,even later than Pb,Zn,W,Sn,Mo mineralizations.In the Periodic Table,C,B,P,Mg and Al belong to Periods 2-3.The mineralizations of these elements mainly took place in Precambrian;Fe,Au,Cu,Pb,Zn,W,Sn,Mo,Hg and Sb belong to Periods 4-6.Mineralizations of these elements mainly took place in the late stage of the evolution of the earth.Uranium（U） belongs to Period 7.The U mineralization in China almost all appeared after mineralizations of W,Sn,Mo,Bi,Fe,Cu,Zn,Nb,Ta and REE.In other words,in the evolutionary history of the earth,the atomic structures of ore-forming elements become more and more complex,while the outer electronic layers increase from 2 or 3 layers（C,B,P,etc.） up to 7 layers（U）.In ore-prospecting,therefore,to look for mineral deposits of the elements in the upper part of the Periodic Table,we should conduct relevant prospecting work in old crustal regions（Precambrian regions）;to look for those in the middle part of the Period Table,we should take into account both old and young crustal regions;to look for those in the lower part of the Periodic Table,we should carry out relevant work in the regions where young geological,tectonic,magmatic and hydrothermal activities are developed.Since Phanerozoic,especially since Late Paleozoic and Mesozoic,further developments of the hydrosphere,atmosphere and biosphere have made the evolutionary tendency further complicated;the formation of sedimentary deposits,especially the recycles of C,H and O,have resulted in the generation of large amounts of coal,petroleum and natural gas.