Abstract

The Mociços Cu-deposit is part of a cluster of ancient copper mines in the Sousel-Barrancos metallogenic belt in the Ossa-Morena Zone at the SW Iberia. The orebodies develop along NNW-SSE quartz-carbonate-sulfides veins with pyrite and chalcopyrite as the main sulfide phases, and ore emplacement has been attributed to copper remobilization from the metasedimentary host-rocks, though no detailed studies were conducted. A novel multi-stage fluid circulation model is hereby proposed, supported by petrography and fluid inclusion data evidencing the P–T–V-x evolution of the deposit. Stage (i) is an early metamorphic stage with a predominance of carbonic fluids, identified in highly deformed milky quartz (Qz_I), with estimated pressures between 338 and 486 MPa compatible to the regional metamorphic events (greenschist facies). Stage (ii) corresponds to a late-metamorphic manifestation of H₂O–NaCl–CO₂ fluids, with low-salinity (eq. w(NaCl) from 0.4 to 5.0%) and CO₂ dominated. Stage (iii) in which ore emplacement took place and is characterized by dominant multisolid H₂O–NaCl hypersaline, halite-bearing fluid inclusions (eq. w(NaCl) from 29.3 to 44.3%) with an H₂O–NaCl–CO₂ endmember and features indicative of magmatic-hydrothermal brines. Many of these inclusions homogenize by halite dissolution, with pressures as high as 320 MPa, and the coexistence of both fluids in the same fluid inclusion assemblages (FIA) could indicate phase separation caused by fluid pressure variations. Although there is no direct evidence of the magmatism responsible for these fluids, the geodynamic settings could favor deep-seated magmatism. Stage (iv) is characterized by low-salinity (eq. w(NaCl) from 0.18 to 15.57%) and low-temperature (68 to 160°C) primary two-phase fluid inclusions hosted by late-stage quartz (Qz_IV), suggesting a late-meteoric fluid circulation phase responsible for the leaching, oxidation and supergene enrichment observed at surficial levels. Throughout the P–T evolution of the system a decrease in pressure and temperature was registered, especially in fluid inclusions hosted in quartz from the sulfide bearing veins, suggesting that the transition from ductile to brittle regimes might have favored ore deposition.

中文翻译：

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负责奥萨-莫雷纳地区（葡萄牙）矿床沉积的多阶段流体系统：铜矿床形成中的制约因素

摘要

Mociços铜矿床是西南伊比利亚Ossa-Morena区Sousel-Barrancos成矿带中古代铜矿群的一部分。矿体沿着以黄铁矿和黄铜矿为主要硫化物相的NNW-SSE石英-碳酸盐-硫化物脉发育，尽管未进行详细研究，但矿床的沉积归因于从准沉积岩中的铜迁移。因此，在岩石学和流体包裹体数据的支持下，提出了一种新颖的多级流体循环模型，证明了矿床P – T – V -x的演化。（i）阶段是早期变质阶段，主要含有碳流体，在高度变形的乳白色石英中被发现（Qz _I），估计压力在338至486 MPa之间，与区域变质事件（绿岩相）兼容。阶段（ii）对应于H ₂ O–NaCl–CO ₂流体的后期变质表现，具有低盐度（当量w（NaCl）从0.4％到5.0％）和CO ₂为主。（iii）阶段，其中发生了矿石入矿，其特征是主要的多固体H ₂ O–NaCl高盐，含盐分的流体包裹体（当量w（NaCl）为29.3％至44.3％）和H ₂ O–NaCl–CO ₂岩浆热液盐水的最终成员和特征。这些夹杂物中的许多夹杂物在高达320 MPa的压力下通过盐岩溶解而均质化，并且两种流体在同一流体夹杂物组合（FIA）中的共存可能表明由流体压力变化引起的相分离。尽管没有直接证据表明岩浆作用是这些流体的原因，但地球动力学环境可能会有利于深部岩浆作用。阶段（iv）的特征是由后期石英（Qz _IV）托管的低盐度（eq。w（NaCl）为0.18至15.57％）和低温（68至160°C）的主要两相流体包裹体。，表明在地表水平观察到晚地流体循环阶段负责浸出，氧化和超基因富集。整个P- Ť在压力和温度的降低被注册，特别是在流体夹杂物托管从硫化轴承脉石英，这表明从韧脆制度的过渡可能具有有利矿石沉积系统的演化。