斑岩铜-金矿床挥发分（S和Cl）来源研究：来自包裹于成矿岩体造岩矿物内磷灰石的限定

Porphyry Cu deposits (PCDs) provide nearly three-quarters of Cu, half of Mo, and important amount of Au to the world, and single deposits can be very large. The huge accumulation of metals in the upper crust is directly associated with the huge amounts of volatiles (S, Cl, CO2, and H2O) released from the PCD system. The volatiles (S and Cl) act both as the agent to precipitate ore minerals and as a primary ligand for transport of ore-forming metals in aqueous solutions to the site of ore deposition, thus understanding the behaviors of volatiles during mineralization are critical to resolve the puzzle of genesis of PCDs. However, the source of these volatiles is still in controversial. Apatite [Ca5(PO4)3(F,OH,Cl)] has been taken as the best mineral that can provide information on volatile concentrations in melts, because it incorporates chlorine, fluorine, and minor amounts of sulfur. However, volatiles in apatite may re-equilibrate with surrounding melt or fluid within a relatively small time interval. Therefore, conclusions inferred from separated apatite grains might be problematically. The most effective way for apatite to maintain their primary chemistry is for them to become as inclusion in other mineral grains, which can chemically isolate apatite grains from any medium for exchange. Therefore, we plan to use apatite grains occurred as inclusions in other minerals, especially plagioclase grains with clearly growth zonation, to address the question of sources and evolution processes in magmas during PCD mineralization. Samples are from ore-forming tonalite and mafic enclaves in the Saindak porphyry Cu-Au deposit, Pakistan.

斑岩铜矿床是全球铜、钼和金的主要来源，故国内外学者对其成因的研究尤为重视。浅部地壳巨量金属的聚集离不开斑岩成矿系统大量挥发性组分（S、Cl、CO2、H2O等）的聚集与释放。挥发组分中的S和Cl在成矿金属元素从源区的抽离，岩浆和流体中的迁移，以及浅部地壳的卸载都起着至关重要的作用，但对它们来源的认识至今仍有较大争议。因此，本项目拟以包裹于成矿岩体造岩矿物内的磷灰石颗粒为研究对象。因寄主矿物的隔离，呈包裹状态的磷灰石可有效地保存其结晶时的原始特征，而不被后期的溶体或流体所改造。因此，依次对包裹于不同结晶顺序的造岩矿物（辉石→角闪石→黑云母→石英）和不同牌号斜长石（正–反环带）内的磷灰石进行研究，可较好地反演出岩浆结晶分异演化过程、镁铁质岩浆的注入和岩浆混合过程中岩浆系统挥发分（S和Cl）含量特征，进而可更准确地限定斑岩铜矿床中挥发分（S和Cl）的来源，及其注入、聚集和释放过程。

斑岩铜矿床是全球铜、钼和金的主要来源，故国内外学者对其成因的研究尤为重视。大型斑岩铜矿离不开斑岩成矿系统大量挥发性组分（S、Cl、H2O等）和巨量金属在浅部地壳的聚集与释放。挥发组分中的S和Cl以及成矿金属元素从源区的抽离，岩浆中流体出溶和迁移，以及浅部地壳的卸载都起着至关重要的作用，但对它们来源的认识至今仍有较大争议。因此，本项目以山达克矿床为研究区，通过岩石学、元素和同位素地球化学，锆石U-Pb和锆石Hf同位素明确了各套岩浆来源和演化机制以及相互间成因联系。在此基础上，以成矿岩体造岩矿物斜长石以及包裹于内的磷灰石颗粒为对象进行原位矿物学研究表明，山达克斑岩矿床下伏岩浆房是通过多期次小体积原始熔体幕式注入形成。斑岩铜矿床形成于深部岩浆房的生长阶段。斑岩铜矿成矿过程中深部岩浆房中S、Cl和Cu等成矿元素释放和再补给过程与岩浆房生长和演化具有耦合关系。岩浆房的生长与成矿岩浆的幕式注入有关，每一次新鲜的母岩浆的注入，都会带来S、Cl和Cu等成矿物质，而这些成矿物质会快速高效地释放到热液流体中，并用于斑岩成矿。一旦新鲜的母岩浆停止注入，即岩浆房停止生长，成矿作用也会随之迅速停止。角闪石、磷灰石和斜长石等多相矿物学研究表明成矿岩浆在合适深度岩浆房达到流体饱和，流体大程度出溶过程中，Cl和S被强烈地分配到出溶的流体相，Cl和S可以形成络合物并从熔体中有效地萃取金属元素至流体相，流体携载成矿物质可随岩浆迁移并在合适的位置卸载成矿，而岩浆在晚期阶段成矿物质已经枯竭，没有成矿能力。