华南加里东期造山型金矿中金的来源——来自浙江诸暨陈蔡杂岩的证据

The Gold Source in Orogenic Gold Deposits of South China in the Caledonian Period:Evidence from Chencai Complex in Zhuji,Zhejiang Province

造山型金矿中金的来源是目前广泛争论的问题,尽管变质成因模式受到了较多的关注,但研究实例还不多。加里东期是华南地区重要的金矿成矿期,浙江诸暨陈蔡杂岩发育了从绿片岩相到角闪岩相的岩石组合,变质时代为加里东期,同时,其变质温度和压力等都已经得到精确厘定,是研究华南加里东期金矿形成与变质作用的关系的理想对象。通过系统采集陈蔡杂岩岩石样品,在详细岩相学研究的基础上,对其中的黄铁矿中的金及亲硫元素进行了激光剥蚀-电感耦合-等离子体质谱(LA-ICP-MS)原位微区微量元素分析。研究结果表明:陈蔡杂岩角闪岩相岩石中有绿泥石,角闪石退变质为黑云母,反映退变质作用中有变质流体的回流。华南加里东期变质过程中,从绿片岩相到角闪岩相的相变过程中金及其他亲硫元素从主要赋存矿物黄铁矿中释放出来,进入变质流体,为江南造山带造山型金矿提供了金属来源。利用硫化物单矿物进行金的含量原位分析是解决变质过程中金活化迁移的重要手段,并提出华南加里东期变质过程中金的来源模式图。

The origin of gold in orogenic gold deposits remains a debated issue now.Although the metamorphic genetic model has attracted much attention,it requires to be further tested by case studies.The Caledonian period is an important gold metallogenic time in South China.The Chencai complex in Zhuji of Zhejiang Province contains greenschist to amphibolite facies rocks with metamorphic age of Caledonian.Meanwhile,the metamorphic temperatures and pressures have been well constrained,which provides an ideal area for testing the above-mentioned metamorphic model.Samples were collected from this complex in the field,and detailed petrographic study on these samples and concentrations of gold and chalcophile elements in pyrites by laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)in situ analyses was conducted.The results show that the Chencai complex amphibolite facies experienced retrograde metamorphism characterized by hornblende transformed to chlorite and biotite,indicating metamorphic fluid reflux.Gold and other chalcophile elements released from pyrites into the metamorphic fluid during the South China Caledonian prograde metamorphism from greenschist to amphibolite facies,which provided a source of metal for the Jiangnan orogenic gold deposits.The in-situ analysis of gold content in sulphide minerals is an important means to resolve the activation and migration of gold during metamorphism.Based on these analyses,a new source model of gold in the Caledonian metamorphic process of South China was proposed.