Impact of sulfide saturation events on the fertility of porphyry-related magmatic system

斑岩铜-(金-钼)矿床是岩浆-热液系统的化石，提供了对我们的社会至关重要的75%的铜和很大一部分其他关键金属(如钼、金、稀土)。前人的研究表明，斑岩型铜(金-钼)矿床是由下地壳原始弧玄武岩分异形成的中-长英质岩浆组成的旋回复活的上地壳岩浆库中喷出的大量热液形成的。岩浆系统在整个跨地壳演化过程中影响矿石成分(如金属、H2O、S、氯)的过程强烈影响其形成经济矿床的能力，并控制成矿岩石的金属特征(即铜/金比)。在岩浆系统跨地壳演化过程中发生的岩浆硫化物饱和事件被认为是控制岩浆系统的丰度(即形成经济斑岩铜(金-钼)矿床的能力)的最重要因素之一。富含亲氯金属(铜、金、铅)和硫的岩浆硫化物的结晶强烈地贫化了这些元素中的残余熔体。岩浆硫化物可以从系统中分馏出来，从而降低岩浆系统的肥力，或者它们可以作为临时存储介质，然后被热液岩浆流体重新活化。因此，岩浆硫化物饱和事件目前要么被认为是有害的，要么被认为是中性的，要么被视为对岩浆系统的丰度有积极影响的过程。这种共识的缺乏阻碍了斑岩型铜(金-钼)矿床新的有效勘探方法的发展。这场争论源于岩浆系统跨地壳演化过程中硫化物和流体饱和事件的困难。目前的项目将通过研究属于Menderes Massif(土耳其西部)和Stikinia Terrane(不列颠哥伦比亚省，加拿大)的两个不同的岩浆-热液系统来弥补这一知识差距。在这两个岩浆系统中，岩浆硫化物饱和事件将通过岩浆硫化物包裹体的研究来识别和表征。这些包裹体将用LA-ICPMS进行化学表征，硫化物饱和事件将使用(I)赋存这些包裹体的斑晶的化学成分和(Ii)共捕获的硅酸盐熔体包裹体的化学成分来确定时间。将利用岩浆硫化物包裹体的硫同位素组成来追踪流体饱和事件，因为它们的硫同位素特征与岩浆系统排出的流体数量直接相关。这种方法从来不适用于与斑岩铜(金-钼)矿床有关的岩浆系统，这将允许明确地评估硫化物饱和事件对岩浆系统的丰度和对已形成的斑岩铜(金-钼)矿床的金属特征的影响。

Porphyry Cu-(Au-Mo) deposits are fossils magmatic-hydrothermal systems that provide 75% of the copper vital to our society and a significant portion of key other metals (e.g., Mo, Au, Re). Previous studies have demonstrated that porphyry Cu-(Au-Mo) deposits are formed by large volume of hydrothermal fluids outgassed from a cyclically rejuvenated upper crustal magma reservoir composed of intermediate to felsic magmas derived from the differentiation of primitive arc basalts in the lower crust. Processes affecting ore ingredients (i.e., Metals, H2O, S, Cl) during the entire transcrustal evolution of a magmatic system strongly influence its capacity to form an economic deposit and control the metal signatures of the mineralized rocks (i.e., Cu/Au ratio). Magmatic sulfide saturation events occurring during the transcrustal evolution of a magmatic system have been suggested to be one of the most important factors controlling the fertility of a magmatic system (i.e., capacity to form an economic porphyry Cu-(Au-Mo) deposits). Crystallization of magmatic sulfides rich in chalcophile metals (Cu, Au, PGEs) and sulfur strongly depletes the residual melt in these elements. Magmatic sulfides can be either fractionated out of the system and in this way reducing the fertility of the magmatic system or they can act as a temporary storage medium and be latter remobilized by hydrothermal magmatic fluids. Therefore, magmatic sulfide saturation events are currently either view as a detrimental, as a neutral, or as a positive process on the fertility of a magmatic system. This lack of consensus hampered the development of new efficient exploration methods for porphyry Cu-(Au-Mo) deposits. This debate is sourced from the difficulty to time sulfide and fluid saturation events during the transcrustal evolution of a magmatic system. The current project will address this knowledge gap by the study of two different magmatic-hydrothermal systems belonging to the Menderes Massif (western Turkey) and to the Stikinia Terrane (British Columbia, Canada). In these two magmatic systems, magmatic sulfide saturation events will be identified and characterized by the study of magmatic sulfide inclusions. These inclusions will be chemically characterized by LA-ICP-MS and sulfide saturation events will be timed using the chemical composition (i) of the phenocrysts hosting these inclusions and (ii) that of co-trapped silicate melt inclusions. Fluid saturation events will be tracked using the sulfur isotopic composition of the magmatic sulfide inclusions, as their sulfur isotopic signature is directly linked to the quantity of fluid exsolved from the magmatic system. This approach never applied to magmatic systems related to porphyry Cu-(Au-Mo) deposits will allow the unambiguous evaluation of the impact of sulfide saturation events on the fertility of magmatic systems and on the metal signatures of formed porphyry Cu-(Au-Mo) deposits.