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

硫化物饱和事件对斑岩相关岩浆系统肥力的影响

• 批准号: RGPIN-2021-02593
• 负责人: Rottier, Bertrand
• 金额: $ 2.19万
• 依托单位: Université Laval
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=755014
• 关键词: Impact; sulfide; saturation; events; fertility

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.

斑岩铜（金钼）矿床是一种化石岩浆热液系统，提供了对我们社会至关重要的75%的铜和重要的其他金属（例如，Mo、Au、Re）。前人的研究表明，斑岩型Cu（Au-Mo）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上地壳岩浆库，经周期性再生，释放出大量热液流体而形成的。影响矿石成分的过程（即，金属、H2O、S、Cl）强烈影响其形成经济存款的能力，并控制矿化岩石的金属特征（即，Cu/Au比率）。在岩浆系统的穿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肥力的最重要因素之一（即，形成斑岩型铜（金钼）矿床的能力）。富含亲铜金属（Cu、Au、PGEs）和硫的岩浆硫化物结晶强烈地消耗了残留熔体中的这些元素。岩浆硫化物可以从系统中分离出来，从而降低岩浆系统的肥力，或者它们可以充当临时储存介质，随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被认为是一个有害的，作为一个中性的，或作为一个积极的过程中的岩浆系统的肥力。这种缺乏共识阻碍了斑岩铜（金）钼矿床新的有效勘探方法的发展。这一争论的根源在于岩浆系统穿壳演化过程中硫化物和流体饱和事件的时间难以确定。目前的项目将通过研究属于Menderes地块（土耳其西部）和Stikinia地体（加拿大不列颠哥伦比亚省）的两个不同的岩浆热液系统来弥补这一知识空白。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。这些夹杂物的化学特征，LA-ICP-MS和硫化物饱和事件将定时使用的化学成分（i）的斑晶托管这些夹杂物和（ii）的共同捕获的硅酸盐熔体夹杂物。将使用岩浆硫化物包裹体的硫同位素组成来跟踪流体饱和事件，因为它们的硫同位素特征与从岩浆系统中溶出的流体的量直接相关。这种方法从来没有适用于岩浆系统有关的斑岩铜-（金-钼）矿床将允许明确的评价硫化物饱和事件的影响，岩浆系统的生育能力和形成的斑岩铜-（金-钼）矿床的金属签名。