Isotopic Geochemistry of Chinese Fluorite Deposits

China is one of the richest countries in the world in terms of fluorite resources. On the basis of host rocks and mineralization patterns, the fluorite deposits in China have been classified into three types: (1) those occurring in Mesozoic volcanic regions, mainly consisting of veinfilling deposits of the quartz-fluorite association (Type I); (2) those occurring in granite areas, chiefly belonging to veinfilling deposits of the quartz-fluorite association or veinfilling or altered-rock deposits associated with Pb, Zn, W, Sn, etc. (Type II); and (3) those occurring in carbonate rocks as bedded deposits of quartz-fluorite, sulfide-fluorite, and quartz-barite-calcite-fluorite assemblages (Type III).

This paper summarizes the characteristics of fluorite deposits in China on the basis of strontium-, hydrogen-, and oxygen-isotopic and geochronological data, as well as geological investigations of deposits from 22 mining districts. δ¹⁸O and δD values of ore-forming fluids are ?10.2 to +3.7‰ and ?77.9 to 41.0‰, respectively, for Type-I deposits, ?13.1 to ?4.9‰ and ?65.5 to ?41.7‰ for Type-II deposits, and -5.6 to +4.3‰ and ?80 to ?29‰ for Type-Ill deposits. Study of the isotopic water-rock exchange indicates that the mineralizing fluids for these types of deposits have been derived mostly from circulating geothermal water that originated from Mesozoic meteoric water. The differences in the isotopic characteristics of hydrothermal systems for various types of deposits depend mainly on isotopic exchange between water and rocks, the water/rock values being 0.05 to 2.0 for Type-I deposits, generally more than 2.0 for Type-II deposits, and 0.5 to 3.0 for Type-Ill deposits.

The ore-forming ages for Type-I and Type-II deposits are roughly separated into three groups—230 to 180 Ma, 120 Ma, and 90 to 60 Ma. These ages successively decrease from northwestern China to southeastern coastal areas.

⁸⁷Sr/⁸⁶Sr values of 0.7306 to 0.7710 (mean 0.7513) from fluorite in the early stage (main mineralization) for Type-I deposits are higher than those from host rocks (0.7081 to 0.7260) during the mineralizing event, and mostly fall in the range of ⁸⁷Sr/⁸⁶Sr values from basement metamorphic rocks (from 0.7455 to 0.9094) during the epoch of mineralization. But the ⁸⁷Sr/⁸⁶Sr values of 0.7102 to 0.7137 (mean 0.7122) for late-stage fluorite and calcite are similar to those of surrounding host rocks. This indicates that the mineralizing materials of early stages in the formation of deposits (Type-I) originated mostly from Precambrian basement metamorphic rocks; those of later stages (Type II) were derived chiefly from host rocks. Type-II and Type-Ill deposits from different mining areas exhibit great variations in ⁸⁷Sr/⁸⁶Sr values, but are quite similar to their host rocks, indicating that the mineralizing materials in Type-II and Type-Ill deposits were derived chiefly from their host rocks.     

Ore-forming timing of polymetallic-fluorite low temperature veins from Central Pyrenees: A Pb,Nd and Sr isotope perspective

Vein fluorite deposits (Tebarray, Lanuza, Bielsa-Parzán, Bizielle and Yenefrito) as well as one MVT-style fluorite mineralization (Portalet) in the Central Pyrenees are the focus in this contribution. These deposits are made up of fluorite, barite, base metal sulphides, calcite, and quartz and are hosted in sedimentary rocks and granites of Palaeozoic age. Generally, these mineral occurrences, typically associated with Late Palaeozoic steeply dipping faults are similar with respect to geologic setting, mineralogy and geochemical trends to other fluorite and base metal veins located in the Central Pyrenees. Veins occurring along such faults most likely represent channelways used by mineralizing solutions that were expelled from the basement. Previous work argued for genetic processes involving circulation of mineralising fluids during the Triassic–Lower Cretaceous period, which is often considered to represent a period of heat, fluid, and mass transfers related to rifting events in the western European basins, which is related to the opening of the Atlantic.A major goal of this study was to decipher the timing of fluid flow and ore formation on the basis of Nd–Sm dating of fluorite sampled from a number of deposits sharing a similar geological framework. No precise age(s) could be obtained due to a scatter in data, but results from the Portalet MVT-style deposit point to a mid-Triassic age (around 220 Ma) for this mineralization. The model that best explains the diagenetic stratabound mineralization at Portalet is gravity-driven fluid flow involving basinal brines during a rifting stage. Indeed, the formation of horst and graben structures during Early Alpine extensional tectonics favoured the infiltration of meteoric water into uplifted blocks, followed by fluid migration through the deeper parts of the basins whereby heat and dissolved components were acquired. This model also explains diagenetic changes recorded in the host limestone at Portalet. Also, overall Pb, Sr and Nd isotopic ratios measured in galena and fluorite suggest that differences in host rock and in the lithology of the basement seem to have exerted control on the chemistry of mineralizing fluids providing each deposit with distinctive characteristics.     

热水成矿作用

本文从热水成矿作用的基本概念、成矿流体地球化学、物理化学与矿床地质等方面对热水成矿作用进行了系统总结，提出热水成矿流体以同生盆地水、表生水包括大洋水为主，在深循环过程中与高温地质体发生作用而获得热量和成矿元素，最后演化为成矿流体；矿化作用主要发生在热水喷流孔附近的物理化学梯度带；对于发生在沉积岩中同生盆地水成因的热水成矿作用具有类似油气藏的生成储集模式，在开放型构造中形成渗透浸染状矿化；在封闭构造中，含矿流体首先集中在构造圈闭中，在构造活动期水爆成矿。热水沉积建造及沉积相带划分是热水成矿作用研究的重要方面，横向上一般划分为硅质岩沉积带、碳酸盐沉积带、硫酸盐沉积带，同时伴随着矿化分带；纵向上分为脉状充填带与喷流沉积带。     

西藏羊八井现代地下热水系统硫矿的成矿作用

通过对羊八井盆地地热流体的地球化学、气体成分、同位素特征以及泉华、岩矿等资料的研究 ,确认该地下热水溶液中的水主要来自大气降水 ,部分来自深部 ;矿质大部分源自对围岩的淋滤和溶解 ,少部分物质 ,如易挥发成分则与岩浆体有关 ;热源则由地壳浅部岩浆体供给。根据羊八井地热水成矿作用特点和矿化分布规律 ,提出成矿区主要位于地热流体卸压排泄系统成矿的论点 ,并建立了羊八井盆地地热水系统成矿概念模型。地热田内自然硫及其它硫化矿物的形成过程中微生物起着重要的作用     

地幔流体在滇西富碱斑岩成岩成矿过程中的作用——地质年代学和同位素地球化学制约

滇西金沙江哀牢山断裂以东广泛发育富碱斑岩型多金属矿床,其富碱斑岩体中有多处产出深源岩石包体。对包体岩石和寄主富碱斑岩及其成矿石英脉的地质年代学研究显示,深源岩石包体的成岩年龄大于寄主富碱斑岩,而富碱斑岩的成岩与成矿是基本同时的。结合铅硅锶钕同位素地球化学研究表明,在富碱岩浆的成岩过程中,伴随富硅成矿流体对围岩和岩体的交代蚀变,并与地壳岩石一定程度混染而实现成矿作用。这种富硅成矿流体作用实质上是地幔流体作用在地壳中成矿作用的延续。据此,从地幔流体交代矿物的结晶年龄(116.0 Ma)到富硅成矿流体年龄(51.2 Ma),揭示地幔流体作用贯穿于富碱岩浆成岩成矿的全过程。正是这一地幔流体作用过程,导致Si、Al、Na、K及其它硅不相容元素和成矿元素富集,进而导致其Sr-Nd同位素特征由亏损地幔向富集地幔过渡,并引起从岩体→围岩对应、从高温→低温的系列成矿效应。也正是这种流体作用,构成滇西新生代广泛成矿的内在统一制约因素和大型-超大型矿床形成的重要地球化学背景。     

Constraints of Sr isotopic compositions of apatite and carbonates on the origin of Fe and Cu mineralizing fluids in the Lala Fe-Cu-(Mo,LREE) deposit,SW China

Numerous Fe-Cu deposits with mineralization styles similar to iron oxide-copper gold (IOCG) deposits form the Kangdian Fe-Cu metallogenic province, southwestern (SW) China. As one of the largest deposits in the region, the ~ 1.0 Ga Lala Fe-Cu deposit is hosted in a Paleoproterozoic volcanic-sedimentary succession named the Hekou Group which is alternately intruded by ~ 1.0 Ga doleritic plutons. This deposit has a paragenetic sequence evolving from Stage I of Na-alteration to Stage II of Fe mineralization, and finally to Stage III of Cu-(Mo, REE) mineralization, coeval with mafic-felsic intra-plate magmatism in the region. This study conducted in-situ Sr isotopic analyses on apatite and carbonate, aiming to resolve the long controversial issue regarding the origin of the Fe and Cu mineralizing fluids in the deposit. Apatite of Stage II has ⁸⁷Sr/⁸⁶Sr ratios varying from 0.71380 to 0.72733, much higher than those of synchronous igneous rocks in the region (0.7074 to 0.7091), but similar to the Paleoproterozoic host rocks (0.71368 to 0.71837 at ~ 1.0 Ga). This similarity indicates that radiogenic Sr of the Fe mineralizing fluid was dominantly sourced from the host rocks. Apatite and calcites of Stage III have ⁸⁷Sr/⁸⁶Sr ratios (0.75758–0.79293) much higher than apatite of Stage II and the host rocks but similar to the Archean basement rocks (as high as 0.80 at ~ 1.0 Ga) beneath the cover of the Yangtze Block, suggesting that the highly radiogenic Sr isotopic composition of the Cu mineralizing fluid was mainly inherited from the old basement rocks. In combination with previous C-O-S isotopic data indicating a magma-hydrothermal origin, it was suggested that the Fe mineralizing fluid was exsolved from a mafic magma that generated the ~ 1.0 Ga doleritic plutons, and inherited radiogenic Sr from the host rocks during fluid-rock interaction. By contrast, the Cu mineralizing fluid might have been sourced from another pulse of magmatic, Cu-Mo-REE- and CO₂-rich fluid which have once interacted with Archean basement rocks prior to mineralization. The source of such a Cu-Mo-REE-rich fluid was not well constrained in current study but was inferred to be exsolved from a hidden felsic magma. We propose that intrusions of the bimodal magmas in Kangdian are responsible for regional hydrothermal circulation which led to Fe-Cu-(Mo, REE) mineralization in the Kangdian province.     

滇西陇川断陷盆地地热水化学特征及循环过程

通过对陇川盆地开展地热地质调查,查清其地热资源分布:盆地内共出露地热点11处,热储结构类型为带状型和层状型,盆地中部为层状型,两侧盆地边缘为带状型,其中北西部受断裂控制明显,南东部受节理裂隙控制明显。其储热层为变质岩及新近系芒棒组的花岗质砂砾岩、细砂岩;地热水受大气降水影响明显,循环深度都在1 600 m以上,大部分在1 800~2 400 m之间,主要来源于深部热源,通过断裂、裂隙及砂砾石孔隙作为导水、储水上涌通道,接收来自山区补给的地下水混合出露于地表,补给距离在1.5 km以上,如南宛河温泉温度最高,地下水循环深度最深,补给距离最远,达10 km;盆地北东和西部水温高,循环深度深。      

The evolution of the Cappadocia Geothermal Province,Anatolia (Turkey): geochemical and geochronological evidence

Cappadocia Geothermal Province (CGP), central Turkey, consists of nine individual geothermal regions controlled by active regional fault systems. This paper examines the age dating of alteration minerals and the geochemistry (trace elements and isotopes) of the alteration minerals and geothermal waters, to assess the evolution of CGP in relation to regional tectonics. Ar–Ar age data of jarosite and alunite show that the host rocks were exposed to oxidizing conditions near the Earth’s surface at about 5.30 Ma. Based on the δ¹⁸O–δD relationhip, water samples had a high altitude meteoric origin. The δ³⁴S values of jarosite and alunite indicate that water samples from the southern part of the study area reached the surface after circulation through volcanic rocks, while northern samples had traveled to the surface after interacting with evaporates at greater depths. REY (rare earth elements and yttrium) diagrams of alteration minerals (especially illite, jarosite and alunite) from rock samples, taken from the same locations as the water samples, display a similar REY pattern to water samples. This suggests that thermal fluids, which reached the surface along a fault zone and caused the mineral alteration in the past, had similar chemical composition to the current geothermal water. The geothermal conceptual model, which defines a volcanically heated reservoir and cap rocks, suggests there are no structural drawbacks to the use of the CGP geothermal system as a resource. However, fluid is insufficient to drive the geothermal system as a result of scanty supply of meteoric water due to evaporation significantly exceeding rainfall.     

Hydrothermal Sedimentary Mineralization of the Super‐large Bamianshan Fluorite Deposit in Zhejiang Province,China

The Bamianshan fluorite deposit is a super-large one recently discovered in Zhejiang Province of China. This paper presents an analysis of its geological background, orebody and ore characteristics, petrochemical characteristics of host rocks, rare earth elements (REE) of rocks and ores, fluid inclusions in fluorite and Sm-Nd isotopic features in an effort to study its sedimentary mineralization. The result shows that the super-large Bamianshan fluorite deposit is of hydrothermal sedimentation genesis, deformed by the later hydrothermal fluid. Integrated with host rocks and orebody characteristics, it is inferred that the deposit originates from the Cambrian sedimentary rocks. And the later magmatic activities deformed some orebodies in different degrees, forming steeply dipping vein orebodies in the tectonic belts regionally.     

The use of vein fluorite as probe for paleofluid REE and Sr-Nd isotope geochemistry: The Santa Catarina Fluorite District, Southern Brazil

Fluorite can be used as a probe for the source of Sr and REE, as well as for the Sr and Nd isotope systematics of mineralizing solutions, allowing characterization of the composition, oxidation state and sources of the fluids. The ⁸⁷Sr / ⁸⁶Sr ratios in vein fluorite from the Santa Catarina Fluorite District, southern Brazil, are low (0.720 to 0.745) relative to those of the majority of host granites at the time of mineralization (90 Ma), but are similar to those of less abundant and less evolved Sr- and Ca-rich granites and plagioclases of the heterogeneous Pedras Grandes granite association. Major contributions of Sr from the unradiogenic Parana Basin rocks (⁸⁷Sr / ⁸⁶Sr_{90 Ma} = 0.705 to 0.718) are unlikely, considering the radiogenic character of the lower ⁸⁷Sr / ⁸⁶Sr end-member in fluorite mixing lines. Estimated fluorite fluid partition coefficients (K_d^Sr-Ca = 0.019 and D^Sr ≈ 600) indicate a Sr / Ca ratio in the fluorite-forming solution of 0.012, and Sr contents of 0.05 to 0.25 ppm, which are similar to those of present-day granitic geothermal waters. Initial Nd isotopic compositions of the vein fluorites (0.5120 to 0.512) are similar to those of the Pedras Grandes granites. The ¹⁴³Nd / ¹⁴⁴Nd_{90 Ma} of the evolved granites of the Tabuleiro granite association, their accessory fluorites and the Parana Basin rocks are considerably more radiogenic (0.5120 to 0.5127) and these are thus considered to be unlikely sources of the fluids. The REE patterns of vein fluorites, normalized to upper continental crust, show a range of LREE-depleted patterns, with highly variable positive and negative Eu anomalies. The host Pedras Grandes granites show flat to slightly depleted UCC normalized LREE patterns with strong negative Eu anomalies. Depletion of the LREE in fluorites resulted from the mobility of HREE fluoride complexes during fluid migration. A REE fractionation model based on ionic potential ratios indicates that Eu³⁺ was stable during fluid migration and fluorite precipitation. The coexistence of pyrite and Eu³⁺ in the mineralizing fluids is consistent with low pH and oxygen fugacities near the hematite-magnetite buffer.     

铜官山矿区金口岭铜金矿床围岩蚀变、成矿物理化学条件及成矿机理研究

本文在研究金口岭铜金矿床的围岩蚀变及其与矿化关系的基础上,运用包裹体矿物学、热力学、稳定同位素地球化学等方法,对矿床形成的物理化学条件、成矿物质来源和成矿机理作了深入研究,论证了成岩成矿物质具同源性。本文强调石英闪长岩株下部发生钾蚀变对矿床的形成起重要作用。     

Isotope Geochemistry of the Xinchang -Yongjia Silver (Lead-Zinc)Ore Belt in Eastern Zhejiang Province

In the Xinchang-Yongjia silver (lead-zinc) ore belt, there mainly occur the large to medium-sized Haoshi, Bamao, Dalingkou and Wubu silver deposits or silver-bearing lead-zinc deposits. On the basis of researches on these typical deposits, the mechanism of leaching-drawing mineralization of Mesozoic geothermal water and the related model are put forward in this paper in the light of the time interval between rock and formation ages as well as hydrogen, oxygen, sulphur and lead isotope geochemical characteristics. The major metallogenic process occurred in volcanic rock layers. The ore-forming fluids are geothermal water coming from meteoric water and circulating at shallow layers. This geothermal water leached and absorbed ore-forming materials from its country rocks during its flowing (such metallogenic elements as silver, lead-zinc and sulphur mainly came from consolidated volcanic rocks), leading to the formation of meso - epithermal silver deposits.     

Metallogeny of the Lannigou Sedimentary Rock-hosted Disseminated Gold Deposit in Southwestern Guizhou Province, China

The Lannigou deposit is a large-sized sedimentary rock-hosted disseminated gold （SRHDG） deposit located in the Youjiang Basin. It is hosted by the Middle Triassic turbidite. Wall rock alterations, including silicification, pyritization, arsenopyritization, carbonatization and argillization, commonly occur along fractures. PGE study demonstrates that either Permian basalts or Triassic ultrabasic intrnsives are unlikely to be the main source of gold mineralization. Coupled with the lack of other nmgmatic activity in the vicinity of the mining area, an amagmatic origin is proposed. Organic matter compositions and GC-MS analysis of the ores and host rocks show that the organics in the ores and the host rocks have a common source; the organic matter in the ores was mainly indigenous. The positive correlation between S2 and Au contents, along with the common occurrence of organic inclusions, suggest involvement of organic matter in the ore-forming process in terms of promoting Au leaching from the source rocks, making colloidal Au migration possible, as well as hydrocarbon reduction of sulphate. Geological and geochemical characteristics of the Lannigou deposit suggest that it was formed through circulation of meteoric water and probably less importantly organic bearing formation water driven by high geothermal gradient caused by late Yanshanian extension, which leached Au from the source bed, and then migrated as Au-bisnlfides and colloidal Au, culminating in deposition by reduction-adsorption and surface complexation of gold onto the growth surface of arsenlan pyrite.     

REE geochemical characteristics of the No. 302 uranium deposit in northern Guangdong, South China

The No. 302 uranium deposit, located in Guangdong Province, is a typical granite-type uranium ore deposit REE geochemical characteristics of the wall rocks, pitchblende, altered rocks, calcite and fluorite from this deposit have been systematically studied in this paper. The result showed that the alkali-metasomatic granites and other altered rocks have the same REE distribution patterns as Indosinian granites. It is indicated that the hydrothermal ore-forming solution had altered the Indosinian granites, and ore-forming materials may directly originate from the Indosinian granites. Calcite and fluorite of different stages are the products derived from the same source but different stages. The evolution and degassing of the mineralizing solution might induce LREE enrichment to varying degree. Mantle fluid and a large volume of mineralizer may be the crucial factors controlling uranium mineralization, and the hydrothermal solution with mineralizer played an important role in U transport and concentration. Meanwhile, the degassing of CO2 might promote U and REE precipitation.     

长白山仙人桥温泉断裂岩溶复合型地热成因模式

长白山仙人桥温泉是我国著名的矿泉水疗养旅游胜地,阐明其成因模式对于温泉区的进一步开发和热水资源的可持续利用具有一定的指导意义。笔者采用地质学、水文地质学和地球物理学结合的方法对其进行了系统研究。结果表明,该区属中低温对流型地热系统,地热成因模式为断裂岩溶复合型。热储层主要为古生界寒武系和奥陶系灰岩,灰岩本身的孔渗条件较差,但后期发育的构造裂缝和溶蚀裂缝却极大地改善了热储层的储集性能;盖层主要为中生界侏罗系安山岩和安山质火山碎屑岩,封闭性较好。长白山一带的大气降水沿侧向断裂和溶蚀裂缝渗入热储层中成为地下水;然后经正常大地热流加热成为地热水,热储温度为89~118℃,循环深度为2 853~3 820m;最终地热水在区内NE向与NW向断裂交汇处富集并沿导水断裂上涌形成温泉。因此,该区断裂交汇和岩溶发育的部位是地热勘探的有利部位。该结论为该区类似地热资源的勘探提供了理论依据。     

锂同位素地球化学在地热流体水岩反应中的应用——以川西现代富锂热泉研究为例

高温流体的化学组成及同位素特征是深部环境信息的重要载体。本文基于锂同位素地球化学方法系统分析了川西现代热泉地热流体的水化学特征、水岩反应过程、补给来源、水岩反应温度及循环深度。研究结果显示,茶洛热泉水化学相类型为HCO₃-Na型,与地表水和冷地下水的HCO₃-Ca型存在明显区别。利用锂同位素温标估算茶洛热泉的水岩反应体系温度为227.80±19.84℃（2σ,n=8）,热循环深度为7348.08m±684.26m（2σ,n=8）。茶洛热泉水化学成分主要受水岩反应控制,处于非平衡向局部平衡过度。高K、Li、F、Cl等与花岗岩岩体有关的特征元素表明水岩反应中以与花岗岩岩体反应为主导,估算其贡献率约为75.34%。矿物饱和指数的计算,显示了热泉水中的白云石、萤石、霞石、方解石处于过饱和状态;钾盐以及大多数样品的石膏、硬石膏处于不饱和状态;石盐则趋近于平衡状态。锂元素浓度及锂同位素分析结果表明,热泉中的锂元素浓度远高于地表水和冷地下水,且富集较轻的锂元素。锂同位素质量平衡拟合估算与茶洛热泉水进行水岩反应的岩体的锂元素浓度为13.43±7.04×10^-6（2σ,n=13）,δ⁷Li_rock值为1.14±2.06‰（2σ,n=13）。岩体深度约6958~7450m。研究成果对于认识地热流体的富锂机理,拓展地热型锂资源的找矿思路均具有理论意义与实际应用价值。

     

国内外太古宇中金矿床的地质及地球化学特征对比兼成因分析

产于太古宇中的金矿床在国内外都属主要金矿类型，虽然有成矿物质都来自含镁铁－超镁铁火山岩的太古宇，但成矿环境在国内外却有重大差异。国外矿床产在地盾上，围岩变质浅，延深大，无垂直分带，金矿物成色高，矿石Ａｕ／Ａｇ值大，放射性成因铅同位素低，成矿压力大，盐度低，成矿时代老（太古宙）。而国内矿床产在活化地台上，围岩变质深，有的有垂直分带性，金矿物成色较低，矿石Ａｕ／Ａｇ值小，放射性成因铅同位素高，成矿压力     

西宁盆地热储构造概念模型的建立

基于西宁盆地地热地质条件的研究,在Donaldson管状模型的基础上,提出的西宁盆地热储构造概念模型是大地热流为热源一低热导率岩层聚热-深循环逐渐加热受迫对流为机制-构造控水控热。进而揭示出,尽管西宁盆地地热异常分布范围较广,但也并非“遍地有热”。在生产实践中,关键是要较为准确地确定地热井的最佳构造部位和找到高渗透率的热储。     

南京汤泉地下热水补给来源与成因模式

南京汤泉地区地下热水资源丰富,阐明其补给来源及成因模式,对于地下热水的科学开发意义重大。采用水化学及同位素地球化学分析方法对其进行了系统研究。结果表明,研究区地下热水与浅层冷水水化学组成差异明显,热储温度为63~75℃,循环深度为1.8~2.3 km。大气降水入渗是地下热水的补给来源,补给高程范围为321~539 m;循环周期为2046~6474 a;地下热水上涌过程中会混入比例为4%~26%的浅部岩溶冷水。经分析,该地热系统成因上属于中低温对流型,补给区主要为老山复背斜构造内的碳酸盐岩裸露区,依靠区域大地热流供热,热储层主要为上震旦统白云岩,盖层为寒武系、白垩系及第四系,地下热水经深循环沿NEE向与NW向断裂交会通道向上运移,并与浅部冷水发生混合,形成本区的地热异常。     

Chemical differences between minerals from mineralizing and barren intrusions from some North American porphyry copper deposits

Major-element analyses (by electron microprobe) and copper contents (by ion-probe) are reported for primary biotite, amphibole, magnetite, pyroxene, ilmenite, sphene and secondary biotite from intrusive rocks from mineralizing and barren stocks. The districts studied include Christmas, Globe-Miami, Sierrita and Tombstone, in Arizona; Bingham and Alta, Utah; Ely, Nevada; and Brenda, British Columbia. Amphiboles from barren rocks are relatively iron-rich and display only minor compositional variation. In contrast, amphiboles from mineralizing rocks span the range from magnesio-hornblende to actinolite, commonly even within one grain. Barren intrusions (type B) that are temporally distinct from mineralizing intrusions, and barren intrusions outside areas of known mineralization have higher Cu contents in their constituent minerals than do mineralizing intrusions. Barren intrusions (type A) that are deep-level temporal equivalents of Cu-bearing porphyritic rocks are depleted in copper. This suggests that copper is abstracted from not only the apical portions of porphyries but from parts of the deeper parent intrusions. The Cu contents of biotites (av. 23 ppm) and magnetites (97 ppm) from barren type B intrusions contrast with those from mineralizing intrusions, with biotites containing 7 ppm Cu and magnetites 3 ppm Cu. Primary amphiboles from all intrusive rock types have low copper contents, typically 2 to 5 ppm. In the continental North American deposits, the amount of copper available by liberation from or non-incorporation into amphibole, biotite and magnetite during magmatic crystallization or the early hydrothermal stage is low, perhaps too low to be the sole source of copper mineralization, unless copper is abstracted from large volumes (∼ 100 km³) of rock. These results contrast with a study of the island-arc porphyry copper at Koloula, Guadalcanal, where it was argued that sufficient copper for mineralization could have been abstracted from relatively small volumes of host rocks that originally contained as much Cu as the contemporaneous barren rock types.