研究生知识库

华南陆块由扬子地块和华夏地块在新元古代时期碰撞拼贴而形成。华南中生代发生了大规模成矿作用，主要在华夏地块一侧（包括扬子地块东部）发生了与花岗岩浆活动有关的钨锡多金属大规模成矿，在扬子地块西南部则发生了大面积低温成矿，形成了全球罕见的世界级多金属成矿省。以往对这些钨锡多金属矿床和低温矿床进行了深入研究，取得了很多重要进展。但是，低温矿床成矿流体的成因和成矿驱动机制一直悬而未决。因为低温成矿区的地表基本没有与成矿同时代的岩浆岩出露，成矿流体中有无岩浆流体加入、成矿是否受岩浆活动驱动是争论的主要问题。He、Ar等稀有气体同位素的地壳和地幔组成很不相同，能对壳幔相互作用进行非常灵敏的示踪。由于地壳和上地幔He的3He/4He比值存在高达近1000倍的差异，加上他们化学上的惰性，其组成不受物理化学条件和流体组成的影响而产生同位素分馏，地壳流体中即使有少量地幔He加入，用He同位素也可方便的判别出来。已有研究表明，华南大面积低温成矿主要发生在130-160Ma和200-230Ma两个时期，与邻区与花岗岩浆活动有关的钨锡多金属大规模成矿时代基本一致。正是基于这些考虑，论文主要选择华南大面积低温成矿域右江盆地矿集区的部分典型低温锑（晴隆锑矿床）、金矿床（水银洞金矿床、丫他金矿床、八渡金矿床）以及华南与花岗岩浆活动有关的部分钨锡多金属矿床（个旧锡多金属矿床、南秧田钨多金属矿床、新寨锡多金属矿床）为对象，针对低温成矿是否受岩浆活动驱动以及钨锡成矿相关花岗岩的成因这两个问题，在野外地质研究的基础上并辅以其它研究，系统开展了矿床He、Ar同位素地球化学的深入研究。其中，为开展这些研究，作者赴英国格拉斯哥大学进行了为期3个月的稀有气体同位素分析测试和研究工作。论文主要取得以下两方面创新成果。1. 揭示华南中生代与钨锡多金属成矿有关的花岗岩具有2种不同成因。（1）150-160Ma和80-100Ma左右的成矿花岗岩。与其有关的钨锡多金属矿床的成矿流体中有大量幔源He和Ar，成矿流体主要是花岗岩浆分异出的岩浆流体，这些花岗岩是壳幔混合作用的产物（即使是S型花岗岩，地幔也为这些花岗岩浆的形成提供了热因而提供了幔源He等挥发分）。（2）200-230Ma左右的成矿花岗岩。与其有关的钨锡多金属矿床的成矿流体中无幔源He和Ar，成矿流体也主要是花岗岩浆分异出的岩浆流体，这些花岗岩是地壳重熔成因的典型S型岗岩（既无地幔物质也无地幔热的贡献）。2. 揭示右江盆地矿集区中低温矿床的成矿流体具有2种不同成因。（1）成矿流体的形成与花岗岩浆活动有关。有两种情况：①包括130-160Ma左右形成的锑矿床，这类矿床是壳幔混合成因花岗岩浆活动驱动大气成因地下水循环而形成，成矿流体的δ34S≈0‰，成矿流体中含地幔He和Ar；②200-230Ma左右形成的卡林型金矿，这类矿床是由典型的S花岗岩浆驱动大气成因地下水循环而形成，成矿流体的δ34S≈0‰，成矿流体中不含地幔He和Ar。（2）成矿流体的形成与花岗岩浆活动无关。包括δ34S值集中在10-20‰左右的卡林型金矿，这类矿床可能是由深循环的大气成因流体侵取地层中的成矿组分而形成，成矿流体中无地幔He和Ar，这些矿床的成矿时代可能是130-160Ma，也可能是200-230Ma。

South China is consists of the Yangtze and Cathaysia blocks which were welded together during the Neoproterozoic time. Large-scale mineralization in South China occurred in Mesozoic to form a famous polymetallic metallogenic province in the world, including numerous low-temperature mineral deposits developed in southwestern part of the Yangtze block and lots of the granite-related W-Sn deposits located mainly in the Cathaysia block. Although previous researches on these deposits have already made important achievements, the problems remain regarding the genesis of ore-forming fluids for the low-temperature mineral deposits. The main issues are whether there were magmatic components in ore-forming fluids of the deposits or the mineralization was triggered by magma due to no coeval igneous rocks with the deposits were found in the mineralized areas.It is well known that the isotopic compositions of He and Ar in crust are totally different from those in upper mantle. For example, there exists about 1000 times difference between 3He/4He ratios of upper mantle and crust, which allows helium to provide unique insight into the processes where mantle or magmatic volatiles have been added to crustal or ore-forming fluids. It has been confirmed that the low-temperature mineral deposits in Yangtze block were formed mainly in two periods, notably at 130-160Ma and 200-230Ma respectively, corresponding to the ages of granite-related W-Sn deposits developed in the Cathaysia block. Based on above background, this paper carried out systematic studies of He and Ar isotopes on representative low-temperature antimony (Qinglong), Carlin-type gold deposits (Shuiyingdong, Yata and Badu) and W-Sn deposits (Gejiu, Xinzhai and Nanyantian), in order to document whether the low-temperature mineralization was triggered by magma and the genesis of granites associated with W-Sn mineralization. For this purpose, the author had gone to University of Glasgow, UK, to analyze He and Ar isotopes for three months. The main conclusions of this paper are as followings.1. There are two types of genesis of the granites associated with W-Sn deposits. The first one is the granites related to the deposits formed at 150-160Ma and 80-100Ma. There exist lots of mantled-derived He and Ar in ore-forming fluids which were dominantly differentiated from granitic magma of crustal-mantle mixture origin. Even the granites are of S-type affinity, the heat, resulting in partial melting of the crustal materials, would be mainly from mantle. The second one is the granites associated with the deposits formed at 200-230Ma. No mantle-derived noble gases were found in ore-forming fluids. The fluids were also differentiated from granitic magma which has typical S-type affinity and be totally unrelated to mantle.2. There are also two types of origins regarding the ore-forming fluids for the low-temperature mineral deposits in Yangtze block. One is the deposits related to granitic magma, which can further divide into two sub-types: (1) Sub-type one is the deposits formed at 130-160Ma, including the Qinglong antimony deposit, which were triggered by crustal-mantle mixing magma. The ore-forming fluids contain mantle-derived He and Ar, and sulfur with δ34S≈0‰. (2) Sub-type two is the Carlin-type gold deposits formed at 200-230Ma. The fluid, triggered by tipical S-type granitic magma, contain no mantle noble gases, but has sulfur with δ34S≈0‰. The second type of origin refers to the low-temperature deposits unrelated to granitic magma. There is sulfur with δ34S ranging from 10‰ to 20‰ and no mantle noble gases in ore-forming fluids for the deposits which were formed by deep circulation of meteoric underground water, and formed either at 130-160Ma or at 200-230Ma.