Magmatic and hydrothermal evolution of the Skouries Au-Cu porphyry deposit, northern Greece

IF 3.2 2区 地球科学 Q1 GEOLOGY Ore Geology Reviews Pub Date : 2024-09-12 DOI:10.1016/j.oregeorev.2024.106233
Alica Höss , Karsten M. Haase , Manuel Keith , Reiner Klemd , Vasilios Melfos , Lisa Gerlach , Fabian Pelloth , Jan J. Falkenberg , Panagiotis Voudouris , Harald Strauss , Tim Baker , Alexandre Tarantola
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Abstract

The Skouries Au-Cu porphyry deposit is located in northern Greece and hosted by quartz monzonites and monzogranites of early Miocene age (∼20 Myr). The host rocks show geochemical similarities to other mafic to felsic intrusions in the district that have a similar strike direction, but which are 6 Myr older and lack evidence of economic mineralization. The Skouries magmas probably formed by fractional crystallization of mafic mantle-derived melts, from which the ore-forming fluids were released during second boiling accompanied by massive feldspar crystallization at ∼65 wt% SiO2. Drill core samples record the dominant potassic alteration with A- and B-type veins, which are locally overprinted by chlorite-sericite alteration and related C-type veins, transitioning into sericitic alteration assemblages and D-type veins. The ore mineralization is characterized by chalcopyrite, bornite, pyrite, magnetite and accessory minerals, such as tellurides and PGE minerals. Incompatible trace element ratios of the host rocks, that are commonly used as tracers of magma fertility (e.g., Sr/Y, La/Sm), vary between the alteration-types and may therefore not generally provide a record of magmatic processes. Fluid inclusion and Ti-in-quartz thermometry yielded a temperature range of 520 to >600 °C for the A-type veins and 420 to 500 °C for the B-type veins. Decreasing fluid inclusion entrapment pressures suggest relatively rapid uplift of the hydrothermal system during the early- to main porphyry stage. Fluid inclusion compositions indicate that early K- and Cl-rich fluids caused the potassic alteration resulting in a strong mobilization of REEs, following a decrease in fluid salinity and temperature with proceeding porphyry evolution. Systematic variations in trace element contents (e.g., As, Ag, Pb) and ratios (e.g., As/Sb, Zn/Pb) of pyrite record fluid temperature changes and suggest early phase separation as a major ore-forming process. The common occurrence of native Au as inclusions in pyrite and chalcopyrite are indicative of early Au oversaturation in the fluid, which we relate to sulfide precipitation and phase separation, destabilizing the AuHS0 or Au(HS)2- complex, leading to the accumulation of Au particles. The formation of such Au colloids in fluids may thus reflect an important step towards the hydrothermal enrichment of Au in porphyry environments.

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希腊北部 Skouries 金-铜斑岩矿床的岩浆和热液演化
斯库瑞斯金-铜斑岩矿床位于希腊北部,由中新世早期(20 Myr)的石英单斜岩和单花岗岩构成。母岩显示出与该地区其他岩浆岩至长英岩侵入体相似的地球化学特征,这些侵入体具有相似的走向,但年代要早 6 Myr,而且缺乏经济矿化的证据。斯库瑞斯岩浆可能是由岩浆幔源熔体的部分结晶形成的,矿石形成流体在二次沸腾过程中被释放出来,同时伴随着大量长石结晶,二氧化硅含量达到 65 wt%。钻探岩芯样本记录了主要的钾盐蚀变,包括 A 型和 B 型矿脉,局部被绿泥石-方镁石蚀变和相关的 C 型矿脉覆盖,然后过渡到绢云母蚀变组合和 D 型矿脉。矿石成矿的特征是黄铜矿、辉铜矿、黄铁矿、磁铁矿和附属矿物,如碲化物和 PGE 矿物。通常用作岩浆肥度示踪剂的母岩不相容微量元素比率(如 Sr/Y、La/Sm)在不同蚀变类型之间各不相同,因此一般可能无法提供岩浆过程的记录。流体包裹体和Ti-in-石英测温得出的温度范围是:A型矿脉为520至600 °C,B型矿脉为420至500 °C。流体包裹体夹持压力的降低表明热液系统在早期至主要斑岩阶段的上升相对较快。流体包裹体成分表明,随着斑岩演化过程中流体盐度和温度的降低,早期富含K和Cl的流体引起了钾盐蚀变,导致了REEs的强烈迁移。黄铁矿微量元素含量(如 As、Ag、Pb)和比率(如 As/Sb、Zn/Pb)的系统变化记录了流体温度的变化,表明早期相分离是主要的成矿过程。黄铁矿和黄铜矿中常见的原生金包裹体表明流体中早期金的过饱和,我们认为这与硫化物沉淀和相分离有关,破坏了 AuHS0 或 Au(HS)2- 复合物的稳定性,导致金颗粒的积累。因此,这种金胶体在流体中的形成可能反映了斑岩环境中金热液富集的一个重要步骤。
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来源期刊
Ore Geology Reviews
Ore Geology Reviews 地学-地质学
CiteScore
6.50
自引率
27.30%
发文量
546
审稿时长
22.9 weeks
期刊介绍: Ore Geology Reviews aims to familiarize all earth scientists with recent advances in a number of interconnected disciplines related to the study of, and search for, ore deposits. The reviews range from brief to longer contributions, but the journal preferentially publishes manuscripts that fill the niche between the commonly shorter journal articles and the comprehensive book coverages, and thus has a special appeal to many authors and readers.
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