滇黔桂地区不同成矿温度热液金矿床磷灰石矿物化学特征:兼论卡林型金成矿流体来源特殊性

Chemical Characteristics of Apatite Minerals in Hydrothermal Gold Deposits with Different Metallogenic Temperatures in the Yunnan-Guizhou-Guangxi Region:A Discussion on the Particularity of Sources of Ore-forming Fluids of the Carlin-type Gold Deposits

滇—黔—桂地区是我国重要的金成矿区之一,分布有众多高温岩浆热液型金(铜)矿床和低温热液型金矿床,但这些矿床的成矿物质来源和形成过程仍存在争议。通过对高温岩浆—热液型金(铜)矿床(姚安金矿床和普朗金铜矿床)和低温卡林型金矿床(八渡和泥堡)中的热液磷灰石进行微量元素统计分析发现:高温富碱斑岩型金(铜)矿床中的磷灰石自形程度较好,具有较高的F和Cl含量,稀土元素呈轻稀土富集,重稀土亏损;相对而言,低温卡林型金矿床中产出的磷灰石自形程度较差,具有相对较低的F和Cl含量,稀土呈中稀土富集模式。另外,磷灰石δEu-δCe图解和球粒陨石标准化稀土元素配分模式揭示卡林型金矿床相对于岩浆热液型铜、金矿床具有更高的氧逸度。结合右江盆地辉锑矿稀土元素地球化学分析,认为磷灰石(包括萤石和方解石)中稀土(MREE)富集特征指示低温成矿流体可能与特殊的盆地基底岩石存在一定联系。综合分析认为:磷灰石在高温—中低温金矿床中具有独特的地球化学特征,能够有效揭示矿床类型及成矿流体演化过程。

Yunnan-Guizhou-Guangxi region,one of the most important gold mineralization areas in China,hosts many high temperature magmatic hydrothermal gold(copper)deposits,such as Pulang gold-bearing porphyry copper deposit,Beiya and Yaoan gold deposits,and low temperature hydrothermal gold deposits,namely carlin-type gold deposit,such as Badu,Nibao and Shuiyindong gold deposits.A lot of chemical studies of minerals,such as magnetite,pyrite and apatite have been carried out,and the abundant mineralogical geochemical data of trace elements in situ have been accumulated.However,the source materials and formation process of the deposits are still be disputed.Therefore,further statistical and comparative analyses of these data may provide a basis for revealing metallogenic information and guiding prospecting exploration.Due to the unique chemical characteristics,apatite can better preserve the important information of magma-hydrothermal evolution process,and is often used to define the fine metallogenic process of ore deposits.In this paper,the trace elements of hydrothermal apatite in high-temperature magma-hydrothermal deposits(Yao’an gold deposit and Pulang gold-bearing copper deposit)and low-temperature carlin-type gold deposits(Badu and Nibao gold deposits)have been collected and analyzed.It is found that the apatite in the high-temperature alkali-rich porphyry gold(copper)deposit is characterized by automorphic shape,high F and Cl contents,enriched LREE,and depleted HREE.In contrast,the apatite in the low-temperature carlin-type gold deposits is characterized by hypautomorphic and xenomorphic shapes,low F and Cl contents,enriched MREE.In addition,theδEu-δCe binary diagram and chondrite-normalized REE patterns revealed that the carlin-type gold deposits have higher oxygen fugacity than magmatic hydrothermal copper and gold deposits.Combined with the geochemical analysis of rare earth elements of stibnite in the Youjiang Basin,it is concluded that the enrichment characteristics of MREE in apatite(including fluorite and calcite)indicate that the low-temperature mineralizing fluid may be related to the special basin basement rock. In conclusion,apatite has unique geochemicalcharacteristics in high temperature-medium and low temperature gold deposits,which can effectively reveal thetype of ore deposit and the evolution process of ore-forming fluid.