Multimillion year thermal history of a porphyry copper deposit: application of U–Pb, 40Ar/39Ar and (U–Th)/He chronometers, Bajo de la Alumbrera copper–gold deposit, Argentina

Application of multiple chronometers (including U–Pb and ⁴⁰Ar/³⁹Ar geochronology and zircon and apatite (U–Th)/He thermochronology) to porphyry intrusions at the Bajo de la Alumbrera porphyry copper–gold deposit, Argentina, reveals a complex history of reheating that spans millions of years. Previous U–Pb geochronology, combined with our new ⁴⁰Ar/³⁹Ar data, shows that the multiple porphyritic intrusions at Bajo de la Alumbrera were emplaced during two episodes, the first at about 8.0 Ma (P2 and associated porphyries) and the second about a million years later (Early and Late P3 porphyries). Complex overprinting alteration events have obscured the earliest hydrothermal history of the deposit. By contrast, ⁴⁰Ar/³⁹Ar data reveal the close temporal relationship of ore-bearing potassic alteration assemblages (7.12 ± 0.13 Ma; biotite) to the emplacement of the P3 intrusions. Consistent with low closure temperatures, younger ages have been determined for associated hydrothermal alkali feldspar (6.82 ± 0.05 Ma and 6.64 ± 0.09 Ma). The temperature-sensitive Ar data also record an unexpected prolonged cooling history (to below 200°C) extending to 5.9 Ma. Our data suggest that the Bajo de la Alumbrera system underwent protracted cooling, after the collapse of the main hydrothermal system, or that one or more low-temperature (~100–200°C) reheating events occurred after emplacement of the porphyritic intrusions at Bajo de la Alumbrera. These have been constrained in part by our new ⁴⁰Ar/³⁹Ar data (including multidomain diffusion modeling) and (U–Th)/He ages. Single-grain (U–Th)/He ages (n = 5) for phenocrystic zircon from P2 and P3 intrusive phases bracket these thermal events to between 6.9 (youngest crystallization of intrusion) and 5.1 Ma. Multidomain modeling of alkali feldspar data (from both igneous and hydrothermal crystals) is consistent with the deposit cooling rapidly from magmatic temperatures to below about 300°C, with a more protracted history down to 150°C. We conclude that the late-stage low-temperature (150 to 200°C) thermal anomaly localized at Bajo de la Alumbrera resulted from radiation of heat and/or fluids sourced from deeper-seated magma bodies, emplaced beneath the deposit. To produce the observed thermal longevity of the porphyry system, magma bodies underlying the Bajo de la Alumbrera deposit must have been repeatedly replenished by new magma batches. Without replenishment, crystallization of the source magma will occur, and heat release will stop, leading to rapid cooling (in less than ten thousand years). The influx of deep-seated magma may have caused the development of late low-temperature hydrothermal alteration assemblages at Bajo de la Alumbrera, at the same time that mineralization formed at Agua Rica, some 25 km away. All available chronologic data for the Bajo de la Alumbrera deposit suggest that the hydrothermal system was active episodically over at least a three-million and possibly up to a four-million-year period. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Outokumpu revisited: New mineral deposit model for the mantle peridotite-associated Cu–Co–Zn–Ni–Ag–Au sulphide deposits

The metaturbidites of the Palaeoproterozoic Jormua–Outokumpu thrust belt in eastern Finland enclose m- to km-scale ultramafic massifs that are distributed over an area of more than 5000 km². These bodies, which almost entirely consist of highly depleted mantle peridotites (now metaserpentinites and metaperidotites), are intimately associated with massive to semimassive, polymetallic Cu–Co–Zn–Ni–Ag–Au sulphide deposits that sustained mining in the region between 1913 and 1988. Currently, one deposit (Kylylahti) is proceeding into a definitive feasibility study emphasising the renewed economic interest for Outokumpu-type deposits.The origin of these Outokumpu-type Cu–Co–Zn–Ni–Ag–Au deposits is now re-interpreted to be polygenetic. First, their formation requires deposition of a Cu-rich proto-ore within peridotitic sea floor at  1950 Ma. Close modern analogues to the proto-ore setting include, for example, the Logatchev and Rainbow fields at the Mid-Atlantic Ridge, where venting of high-T–low-pH hydrothermal fluid resulted in accumulations of Cu–Zn–Co–Ag–Au sulphides on serpentinised ultramafic seafloor. Second, the Ni-rich composition of Outokumpu sulphide ores calls for a separate source for nickel: Some 40 Ma after the deposition of the Cu-rich proto-ore – concomitant with the obduction of the ultramafic massifs – disseminated Ni sulphides formed through chemical interaction between obducting peridotite massifs and adjacent black schists. This process was related to listwaenite–birbirite type carbonate–silica alteration at margins of the ultramafic massifs. Due to this alteration, silicate nickel was released from the primary Fe–Mg silicates and redeposited as Ni sulphides in the alteration fringes of the massifs.We propose that syntectonic mixing of these two “end-member” sulphides, i.e., the primary Cu-rich proto-ore and the secondary Ni-sulphide disseminations, resulted in the uncommon metal combination of the Outokumpu-type sulphides. Late tectonic solid-state re-mobilisation, related to the duplexing of the ore by isoclinal folding, upgraded the sulphides into economic deposits.     

浙江平水铜矿细碧角斑岩锆石LA-ICP-MS U-Pb 年龄及其地质意义

浙江平水铜矿位于钦杭成矿带北东段浙西北地区,钦杭成矿带大致自西南端的广西钦州湾、经湘东和赣中延伸到东北端浙江杭州湾,在这条长约2000 km的古板块结合带上,已探明的大、中型矿床达400余处,其中包括德兴、银山、金山、永平、东乡、芙蓉、黄沙坪、柿竹园、芙蓉、锡矿山、水口山、黄沙坪、东坡、佛子冲等大型—超大型金属矿床（田）（杨明桂 等, 2009;毛景文等, 2011）。浙西北地区也位于成矿地质条件优越的钦杭成矿带北东段,但是,区内目前仅发现了中型的平水铜矿、小型的建德铜矿和小型的璜山金矿等;浙西北地区矿化异常和矿化点非常发育,具有进一步寻找大型矿床的潜力。平水铜矿已连续开采了30余年,前人对平水铜矿在地质特征、成矿流体、矿床成因及成岩成矿年代学等方面已经进行了大量、详细的研究（Chen等, 2015）,但主要集中在矿床成因和成矿模式等方面;而在某些方面研究依旧薄弱,制约区域找矿,如：与成矿关系密切的细碧角斑岩的成岩时代以及成矿构造背景等方面仍没有最终确定。因此,本文选择浙西北地区的平水铜矿,对其细碧角斑岩采用精确的LA-ICPMS 锆石U-Pb法进行年代学制约,揭示浙西北地区平水组细碧角斑岩的成岩时代,为找矿勘查提供依据。     

三江中段铜多金属矿床流体成矿作用:微量元素地球化学证据

研究区属"三江成矿带"中段,包含三个不同的地质构造单元,由西向东依次为金沙江混杂岩带、中咱地块、义敦岛弧带。本文通过对这三个构造单元中代表性铜多金属矿床中热液石英脉进行系统的采样和微量稀土元素分析,讨论了各构造单元中石英脉的微量及稀土元素地球化学特征及分布模式,在此基础上结合研究区的地质背景及演化,进一步讨论石英脉中微量元素的指示意义。结果表明:1)研究区石英脉中Cu、Zn等成矿元素与亲岩浆元素呈较好正相关,指示成矿与岩浆活动的联系,微量元素地球化学特征指示中咱地块成矿流体与岩浆活动的联系较为密切;2)中咱地块石英脉稀土元素地球化学特征与义敦岛弧带和金沙江混杂岩带成矿流体差异较大,中咱地块流体稀土元素接近于地幔的稀土组成特征,稀土元素配分曲线为近于水平的平缓曲线,稀土元素特征参数表明形成于相对还原的环境,反映出深部来源很可能是中咱地块成矿流体的主要物质来源;3)石英微量元素地球化学特征的研究为本区区域构造演化提供了佐证,金沙江混杂岩带和义敦岛弧带的成矿流体特征较为相似,而在中咱地块与扬子陆块夹持间形成的义敦岛弧带成矿流体与中咱地块存在较大的元素地球化学差异。本文通过对石英的微量元素、稀土元素地球化学特征的研究为该区的区域成矿特征、热液流体成因和构造演化提供了证据,并对西南三江地区的找矿理论提出了建议。     

斑岩型铜矿床成矿过程中铜的迁移与沉淀机制研究新进展

作为主要铜源的斑岩型铜矿床一直是研究、生产部门关注的热点。依据多年研究成果和大量文献资料,并以德兴斑岩铜矿研究新成果为实例,综述了斑岩铜矿矿质迁移沉淀机制研究的新进展,包括铜的迁移形式和演化,流体演化对铜络合物作用,铜在熔体相、流体相和晶体相配分以及铜居留场所和形式等。     

河南水洞岭铜多金属矿床地球化学异常特征及找矿标志

水洞岭铜多金属矿床的岩石和土壤地球化学试验研究,表明岩石和土壤中Ｃｕ、Ｐｂ、Ｚｎ、Ａｓ、Ｓｂ、Ｈｇ、Ｃｄ、Ｂｉ、Ｍｏ元素异常清晰,含矿岩系地球化学演化与元素组合变化的一致性,提出Ｃｕ、Ｐｂ、Ｚｎ、Ａｓ、Ｓｂ、Ｈｇ、Ｃｄ、Ｂｉ、Ｍｏ元素可以作为指示元素,并建立了矿床的岩石、土壤地球化学异常概念模式。     

Evidence for Strong Copper(I) Complexation by Organic Ligands in Seawater

Thiols like glutathione and cysteine form such stable complexes with copper(I) that they preclude the presence of copper(II). Conventionally seawater is titrated with copper(II) whilst monitoring the labile or reactive copper concentration by voltammetry or with other techniques, to determine the concentration of copper(II) binding complexing ligands in seawater. Titrations of seawater to which copper(I) binding ligands have been added reveal that the copper(I) binding ligands are detected when seawater is titrated with copper(II). The copper(II) in seawater is reduced to copper(I) within 2 to 40 minutes depending on the nature of the copper(I) binding ligand. The titrations of seawater with copper(II) thus give a response to the presence of copper(I) binding ligands indiscernible from that for copper(II) binding ligands. The stoichiometry of the detected apparent ligand concentrations for given concentrations of glutathione and cysteine suggest that 2 : 1 (thiol : Cu) complexes are formed. This was confirmed using voltammetry of free glutathione. Values of 21.2 and 22.2 were found for log _CuL for glutathione and cysteine respectively (for the reaction of Cu + 2L CuL₂). The complex stability is similar to that of natural organic species in the oceanic water column. The high stability of the copper(I) complexes was apparent from values of 32.1 and 32.6 for log Cu(I)L2 (for the reaction Cu⁺ + 2L CuL₂) for the copper(I) complexes with glutathione and cysteine in seawater. Glutathione and other thiols are common in the marine system including the water column. It is therefore possible that at least some of the ligands detected in seawater, and previously assumed to be copper(II) binding ligands, are in fact strongly complexed as copper(I). The copper(I) oxidation state may thus be stabilised in seawater.     

论中国铜矿的勘查战略

铜是我国最重要、最紧缺的矿产资源之一。在分析我国铜矿资源的严峻形势后，提出铜矿勘查的主攻方向是特提斯－喜马拉雅成矿带、次为荒漠区普查及老矿带（区）挖潜。在具体的普查工作中，注意矿种、矿床成因类型单矿向矿带（田）及小矿向大矿的“转化”，以扩大普查效果。为弥补铜矿勘查资金的严重不足，应实施金铜并举、以金养铜的普查方针。     

云南大姚凹地苴铜矿床数学模型的建立

大姚铜矿是我国重要铜矿山，对该矿床的最大矿体之一Ⅱ-1号矿体进行了研究，在地质规律研究的基础上，收集了与该矿体相关的铜、银品位数据，建立原始资料数据库，并对所收集的数据进行了可靠性讨论；对9061件铜样品和4160件银样品进行了统计分析，结果表明，铜、银品位服从对数正态分布；铜、银共生相关关系，为弱相关关系，需要分别建立其数学模型。计算了铜、银走向、倾向、厚度方向及平均实验变异函数，并进行了理论拟合和验证，结合矿体的地质特征对获得的参数进行了讨论。     

Copper in the resurrection fjord, Alaska

Copper concentrations have been measured in more than 200 samples collected from an Alaskan fjord and continental shelf and slope regions in the northwestern Gulf of Alaska. Concentrations were lowest (2·1 nmol kg⁻¹) at depths of 400–1000 m in the continental slope waters of the Gulf of Alaska. Copper increased systematically with decreasing salinities shoreward to concentrations >30 nmol kg⁻¹ in fjord surface waters during summer months of high freshwater runoff. Copper concentrations increased with depth at an inner fjord station where deep basin waters have restricted circulation, and these data together with surface (<5 cm) pore water copper concentrations (mean=122 nmol kg⁻¹) about an order of magnitude higher than bottom water copper concentrations are indicative of a flux of copper across the sediment-seawater interface. This latter was estimated at 32±12 nmol cm⁻² annually, and represented less than 20% of the annual input to fjord surface water (228–411 nmol cm⁻²) added during summer months. Mass balances in bottom waters indicate a vigorous recycling of copper with a residence time estimated at 21±11 days. Most copper that is remobilized in surface sediments is returned to bottom waters and little (3%) is removed by subsequent diagenetic reaction in the buried sediments. However, an estimate of copper accumulating in anoxic fjord sediments was comparable with copper added to fjord surface waters suggesting that input-removal reactions rather than internal cycling controls copper geochemistry in this estuary.