Cu, Mn, and Ag mineralization in the Quebrada Marquesa Quadrangle, Chile: the Talcuna and Arqueros districts

The Quebrada Marquesa Quadrangle in Chile exhibits a series of mineralizations comprising manto-type manganese and copper deposits of Lower Cretaceous age, and copper and silver veins of Tertiary age. The deposits are hosted by volcanic and volcaniclastic units of the Arqueros (Hauterivian-Barremian) and Quebrada Marquesa (Barremian-Albian) Formations. Three episodes of manganese mineralization (Mn_1-3) are recognized within the study area. Hydrothermal activity leading to episodes 1 and 3 was of minor importance, while the second one (Mn₂) gave rise to major manto-type deposits of both manganese and copper in the Talcuna mining district. Extensional faulting during Tertiary time resulted in block faulting and the unroofing of the oldest andesitic volcanics and marine sediments (Arqueros Formation). This episode was accompanied by magmatic and hydrothermal activity leading to vein formation in the Arqueros (Ag) and Talcuna (Cu) districts. The latter veins cross-cut the previous manto-type copper deposits. Ore mineralogy is similar in both styles of mineralization (manto- and vein-type) and consists mainly of chalcopyrite and bornite, with variable amounts of galena, tetrahedrite (vein-related), chalcocite, sphalerite, pyrite, hematite, digenite and covellite. Alteration processes at Talcuna can be divided into two categories, those related to the Lower Cretaceous manto-type episode (LK alteration: chlorite-epidote-calcite-albite, prehnite, zeolite), and those associated with the locally mineralized normal faults of Tertiary age (Tt alteration: chlorite-calcite, sericite). The Arqueros silver veins display an ore mineralogy consisting of arquerite, argentite, native silver, polybasite, cerargyrite and pyrargyrite-proustite; associated alteration includes strong chloritization of the country rock. The manto-type deposits formed from fluids of salinity between 11 and 19 wt.% NaCl equivalent and temperatures between 120 and 205 °C. Mineralizing fluids during the vein-type stage circulated at lower temperatures, between 70 and 170 °C, with salinity values in a wide range from 3 to 27 wt.% NaCl equivalent. This distribution of salinities is interpreted as the result of the complex interplay of two different processes: boiling and fluid mixing; the former is considered to control the major mineralogical, textural and fluid inclusion features of the vein-type deposits. We suggest that the Lower Cretaceous mineralization (manto-type stage) developed in response to widespread hydrothermal activity (geothermal field-type) involving basinal brines. Received: 18 July 1997 / Accepted: 28 January 1998     

Gold and copper mineralization at the El Indio deposit, Chile

A Middle Tertiary volcanic belt in the High Andes of north-central Chile hosts numerous precious- and base-metal epithermal deposits over its 150 km north-south trend. The El Indio district, believed to be associated with a hydrothermal system in the late stages of development of a volcanic caldera, consists of a series of separate vein systems located in an area of 30 km² which has undergone intense argillic-sericitic-solfataric alteration. The majority of the known gold-copper-silver mineralization occurs within a structural block only 150 by 500 m in surface area, with a recognized vertical extent exceeding 300 m. This block is bounded by two high-angle northeast-trending faults oriented subparallel to the mineralized veins.Hypogene mineralization at El Indio is grouped into two main ore-forming stages: Copper and Gold. The Copper stage is composed chiefly of enargite and pyrite forming massive veins up to 20 m wide, and is accompanied by alteration of the wall rocks to alunite, kaolinite, sericite, pyrite and quartz. The Gold stage consists of vein-filling quartz, pyrite, native gold, tennantite and subordinate amounts of a wide variety of telluride minerals. Associated with this stage is pervasive alteration of the wall rocks to sericite, kaolinite, quartz and minor pyrophyllite. The transition from copper to gold mineralization is marked by the alteration of enargite to tennantite and by minor deposition of sphalerite, galena, huebnerite, chalcopyrite and gold. Mineral stability relations indicate that there was a general decrease in the activity of S₂ accompanied by variations in the activity of Te₂ during the Gold stage.Fluid-inclusion data show homogenization temperatures ranging from about 220 to 280°C, with salinities on the order of 3–4 eq. wt. % NaCl for the Copper stage. The Gold-stage inclusions indicate a similar range in homogenization temperatures, but significantly lower salinities (0.1–1.4 eq. wt. % NaCl). Fluid inclusions of transition minerals show a weak inverse relationship between homogenization temperatures (190–250°C) and salinities (3.4–1.4 eq. wt. % NaCl), which may represent mixing of hotter Gold-stage fluids with cooler late-Copper-stage fluids. No evidence of boiling was found in fluid inclusions, but CO₂ vapor-rich inclusions were identified in wall-rock quartz phenocrysts which pre-date copper and gold mineralization.Mineral stability calculations indicate that given a fairly restricted range of solution compositions, the Copper-, Transition- and Gold-stage minerals at El Indio could have been deposited from a single solution, with constant total dissolved sulfur which underwent reduction through time. Limited sulfur-isotope data indicates that pyrite from the Copper stage was not in isotopic equilibrium with Copper-stage alunite or Transition-stage sphalerite. The sulfur-isotope and fluid-inclusion data indicate that two fluids with comparable temperatures but different compositions flowed through the El Indio system. The earlier fluid deposited copper attended by sericite-alunite-kaolinite alteration, and later epithermal fluids deposited gold with quartz-sericite-kaolinite-pyrite alteration.     

A multivariate statistical study of copper mineralization in the central section of Mosaboni Mine, Eastern Singhbhum, India

A multivariate statistical analysis was carried out with log-transformed values of Cu, Ni, Co, Pb, Zn, Ag, Cr, Mn, Ca, and Sr in several sets of samples collected across the mineralized base metal zone in sheared soda granite, feldspathic schist, and chlorite schist from the central section of Mosaboni Mine of the famous Singhbhum Copper Belt of eastern India. Linear correlation coefficient matrices of two sets of ore samples (>0.5% Cu)—one from levels 18 and 21 and the other from levels 25 and 28—indicate two well-defined and distinct clusters comprising Cu, Ni, Co, Pb, and Zn on one hand and Ca, Sr, and Mn on the other. Varimax-rotatedR-mode factor analysis of two above-noted sample sets, taken along with available geologic information, indicates that over 80% of the variability in data matrices for 9–10 elements can be accounted for by four distinct processes: (a) an early phase of copper mineralization which apparently replaced Mn, Ca, and Sr in the host rock; (b) a silicate-cum-oxide phase of crystallization/recrystallization of host rock; (c) remobilization of sulfide-forming ore elements (Cu, Ni, Co, Pb, and Zn); and (d) a phase of mineralization of Ag which appears to have replaced Cr, Ca and Cu. Process (c) was quantitatively most important. Factor score studies are suggestive of preferred introduction of Ni, Co, Pb, and Zn along central parts of preexisting copper-mineralized zones.     

Relationship of antimony with gold mineralization in the ore districts of Eastern Kazakhstan

In Eastern Kazakhstan, Sb mineralization is the most widespread in the Irtysh and Bakyrchik ore districts of the West Kalba gold-bearing belt. It is spatially related to disseminated gold-sulfide ores at some deposits and is structurally and spatially isolated at others. Disseminated gold-sulfide mineralization is localized in Carboniferous carbonaceous-terrigenous carbonate rocks. It is marked off by zones of dynamic metamorphism and foliation and is characterized by the ribbon-like-lenticular morphology of ore deposits. Later Sb (predominantly, quartz-antimonite) mineralization is formed in an extension setting as brecciated/veined ores. In combination with gold-sulfide ores, Sb mineralization is more diverse. For example, microparageneses with berthierite, native Sb, aurostibite, ullmannite, jamesonite, and tetrahedrite coexist with pocket-vein quartz-carbonate-antimonite mineralization in the gold-sulfide ores of the Suzdal’skoe deposit. Also, Sb-containing minerals such as arsenopyrite and pyrite are observed. Two temperature regimes of mineralization are established here: 418-300 °C for gold-polysulfide mineralization and 280-200 °C for later Sb mineralization. The isotopic composition of antimonite sulfur at the Suzdal’skoe, Zherek, Zhanan, Bakyrchik, and Dal’ny I deposits shows close values within the interval 5³⁴S of -3.8 to 2.5%c, suggesting its great-depth origin. No visible gold is found in the antimonite of the quartz-antimonite veins, but atomic-absorption analysis reveals few ppm or more gold. Point X-ray analysis indicates the possible presence of the so-called “invisible” gold. Microstructural observations, temporal relationships of the parageneses, and studies of gas-liquid inclusions at the Suzdal’skoe deposit permit assigning Sb mineralization to the second productive gold-polysulfide stage of the ore deposition. The late antimonite stage of mineralization is separated from the gold-polysulfide stage by 7 Myr long intramineralization tectonic shifts. Gold-polysulfide mineralization (248.3 ± 3.4 Ma) was synchronous with Triassic tectonomagmatic activity.     

智利Candelaria-Punta del Cobre铁氧化物铜金矿床地质和成矿作用

智利Copiapó附近海岸东部边缘有一宽5km、长20km的铁氧化物铜金矿床带,包括Candelaria矿床和位于其北东方向3km处的Punta del Cobre矿集区的中小型矿床。初步估计,该成矿带的铜矿石资源量可达7×108~8×10~8t(含铜量1%)。矿石矿物主要为黄铜矿、黄铁矿、磁铁矿、赤铁矿。矿石产状为脉状、角砾状、细脉状等。含矿围岩主要为Punta del Cobre组的火山岩及火山碎屑岩。该矿带中大部分大型矿脉位于北西—北北西向高角度脆性断层与块状火山岩和火山碎屑岩接触带交汇处。Candelairia矿区主要发育黑云母-钾长石±钙角闪石±绿帘石蚀变矿物组合。在Punta del Cobr矿集区,矿床深部的矿石围岩蚀变情况与Candelairia地区一致,但是浅部的矿石赋存于黑云母-钾长石或钠长石-绿泥石±方解石蚀变带中。     

钠长岩类地质地球化学特征及变质变形与铜矿的形成——以四川会理拉拉铜矿床为例

本文论述了拉拉铜矿区钠长岩类的地质地球化学特征及变质变形与铜矿的形成。伴随前寒纪的构造运动,拉拉地区经历了NWW向的剪切变形,使钠长岩产生碎裂-糜棱岩化作用,形成碎裂结构、碎斑结构,显微眼球构造、压力影、云母鱼等。这些结构构造的形成使岩石孔隙度增加,起到扩容作用。由沿近东西向主断裂侵位的辉绿辉长岩体提供的含矿流体及区域变质中产生的变质热液沿钠长岩的碎裂-糜棱构造充填交代,在其产生多种蚀变的同时,铜、钼、钴硫化物沉淀成矿,形成钠长岩型浸染状铜矿石或脉状-网脉状铜矿石。在金云母化较强地段,在变质作用下,形成片岩型铜矿石。因而总体上,拉拉铜矿属动力变质热液型铜矿床。     

东天山自然铜矿化带玄武岩的起源、演化及成岩构造背景

新疆东天山地区与玄武岩有关的自然铜矿化带位于东天山觉罗塔格构造带内,自西向东有十里坡、黑龙峰、长城山、东尖峰等主要矿(化)点,自然铜矿化主要发育在玄武岩、杏仁状玄武岩及凝灰岩夹层中。本文基于玄武岩的地球化学特征,研究东天山自然铜矿化带玄武岩是否与地幔柱有关、岩浆源区性质、岩浆演化、成岩构造背景等问题。研究显示,东天山自然铜矿化带玄武岩与地幔柱岩浆活动无直接关系,整个天山地区是否存在石炭-二叠纪地幔柱岩浆活动也需要进一步的研究; 玄武岩起源于亏损岩石圈地幔,是演化岩浆的产物; 演化的玄武质岩浆形成后,在岩浆房中或上升至地表的过程中没有发生明显的分离结晶作用,也没有受到明显的地壳物质混染; 与玄武岩对应的地幔橄榄岩平衡原生岩浆演化的高镁岩浆的产物,可能为东天山地区与铜镍硫化物成矿有关的基性-超基性岩,指示这些铜镍硫化物矿床可能与地幔柱岩浆活动也没有关系; 玄武岩形成于新疆北部后碰撞构造阶段的伸展期,是在拉张应力体制下,由于软流圈上涌导致岩石圈地幔部分熔融而形成。     

Distribution of copper, zinc, lead and cadmium concentrations in stream sediments from the Mapocho River in Santiago, Chile

The Mapocho river, which crosses downtown Santiago, is one of the most important rivers in contact with a population of about six million inhabitants. Anthropogenic activities, industrialization, farming activities, transport, urbanization, animal and human excretions, domestic wastes and copper mining have affected the river, contaminating it and its sediments with heavy metals. Concentration and distribution of Cu, Zn, Pb and Cd were studied with the purpose of determining their bioavailability and their relation with the characteristics of the sediments. Freshly deposited seasonal sediments were collected from 0–8 cm depths from 6 locations (S₁ to S₆) along the 30-km long channel length, in the four seasons of year on the following dates: May 2001 (D₁, autumn); August 2001 (D₂, winter); October 2001 (D₃, spring) and January 2002 (D₄, summer). The dried samples were sifted to obtain the < 63-μm sediment fraction, since it has been shown that large amounts of heavy metals are bound in the fine-grained fraction of the sediment. Cu and Zn were analyzed by atomic absorption spectrophotometry and Pb and Cd by square wave anodic stripping voltammetry. The highest concentrations of Cu (2850 μg g^− 1) were found in the northern part of the river (S₁, average D₁–D₄), near the mountains and a copper mine, and then decreased downstream to 209 μg g^− 1 (S₆). Total Zn showed an irregular variation, with higher values at S₁ (1290 μg g^− 1) and high values in some winter sampling (1384 μg g^− 1 S₄, S₅–D₂). Pb showed different trends, increasing from S₁ to S₆ (17 to 61 μg g^− 1), with the highest values in the summer samples (83 μg g^− 1, S₄–S₆, D₄), and total Cd increased slightly from mean values of 0.2 and 0.5 μg g^− 1. Partition into five fractions was made using Tessier's analytical sequential extraction technique; the residue was treated with aqua regia for recovery studies, although this step is not part of the Tessier procedure. The results show that Cu, Zn and Pb in the sediments were dependent on the sampling places along the river, and variation in two years was low (D₁–D₄). The highest values of total organic matter, carbonate and conductivity were found in S₆, which has the smallest size particles, while at S₁ the sediments were predominantly sand and contain larger amounts of silica. Cu associated with carbonate decreased gradually from 58% (1771 μg g^− 1, S₁) to 16% (32 μg g^− 1, S₆); Cu bonded to reducible fraction was almost constant (33% to 37%), and Cu associated with oxidizable fraction increased from 7% (S₁) to 34% (S₆), but copper content was lower (214 to 68 μg g^− 1). Zn had a similar fractionation profile. However, Pb bound to oxidizable fraction did not show significant percent variation along the river (20% to 19%), but the amount bounded was 4 to 12 μg g^− 1. The residual fraction increased from 24% to 41% (5 to 25 μg g^− 1, S₁ to S₆). The distribution of Cd in the sediment was almost independent of the sampling stations and was bound to carbonate, reducible and residual fraction in similar proportion. Cu and Zn at S₁ were mainly bound to carbonates and reducible phases with 91% and 73% (2779 and 965 μg g^− 1, respectively), and with a change in the pH and/or the redox potential of the sediment–water system, these contaminants could easily enter the food chain. In S₆ the amount of Cu and Zn in these phases was 50% and 53% (100 to 313 μg g^− 1, respectively).     

月山地区铜成矿作用的同位素地球化学研究

月山地区矽卡岩型和热液脉型铜矿床氢、氧、硫、铅、和硅笔同位素组成及演化的特征显示，区内具工业价值铜矿的成矿物质主要由闪长质岩浆经熔－流分离作用提供，主要成 在放阶段的成矿热液以岩浆水为主，地矿中晚期大气降水混入量逐渐增多，三叠系和部分前三叠系提供了部分硫源和少量成矿物质。     

Re–Os isotope systematics for the Lince–Estefanía deposit: constraints on the timing and source of copper mineralization in a stratabound copper deposit, Coastal Cordillera of Northern Chile

The Lince–Estefanía stratabound copper deposit in the Michilla district is one of the most important deposits in the Coastal Cordillera of northern Chile and is one of the most representative of this type of deposit. Chalcocite and bornite characterize the main stage of hypogene copper sulfide mineralization. Rhenium and osmium isotopes are used here to constrain the age of hypogene mineralization and the source of osmium contained in these ore minerals. A Re–Os isochron yielded an age of 160±16 Ma (2σ), with an associated initial ¹⁸⁷Os/¹⁸⁸Os ratio of 1.06±0.09 (mean square of weighted deviates=1.8). This age is consistent with available geochronological data from volcanic rocks that host the mineralization and associated alteration phases. The high initial ¹⁸⁷Os/¹⁸⁸Os ratio indicates a lower crustal component for the source of Os and, by inference, the Cu sulfides that contain this Os. Late hematite occurs as an isolated phase or, more commonly, is associated with the chalcocite–bornite and supergene chalcocite–covellite associations. Analyses performed on pure hematite indicate a disturbance of the Re–Os system, and hence, this mineral phase is not useful as a Re–Os geochronometer.     

Pliocene lahar deposits in the Coastal Cordillera of central Chile: Implications for uplift, avalanche deposits, and porphyry copper systems in the Main Andean Cordillera

Lahar deposits occur within a shallow marine sedimentary succession of the Pliocene La Cueva Formation in the Coastal Cordillera of central Chile (33°40′–34°15′S). Provenance studies of the abundant volcanic material in the lahar deposits suggest that they derive from denudation by mass wasting of Oligocene–Miocene volcanic rocks on the western slopes of the Main Andean Cordillera at the same latitude. Pliocene rock debris deposits preserved in the region of El Teniente (34°S) and scattered along the westernmost part of the Andes of central Chile indicate catastrophic erosive events related to the rapid uplift of the cordilleran block. This rock debris was deposited by avalanches and transformed further downslope into lahars by dilution with stream water. Lahars were channeled along the ancient drainage system that reached a shallow Pliocene sea at the site of the present Coastal Cordillera. The exceedingly rapid exhumation of active porphyry systems during the Early Pliocene in this part of the Andes may have played a role in affecting hydrothermal processes, brecciation, and diatreme formation at the porphyry systems of El Teniente and Río Blanco–Los Bronces.     

Paleowetlands and regional climate change in the central Atacama Desert, northern Chile

Widespread, organic-rich diatomaceous deposits are evidence for formerly wetter times along the margins of the central Atacama Desert, one of the driest places on Earth today. We mapped and dated these paleowetland deposits at three presently waterless locations near Salar de Punta Negra (24.5°S) on the western slope of the Andes. Elevated groundwater levels supported phreatic discharge into wetlands during two periods: 15,900 to ~ 13,800 and 12,700 to ~ 9700 cal yr BP. Dense concentrations of lithic artifacts testify to the presence of paleoindians around the wetlands late in the second wet phase (11,000?-9700 cal yr BP). Water tables dropped below the surface before 15,900 and since 8100 cal yr BP, and briefly between ~ 13,800 and 12,700 cal yr BP. This temporal pattern is repeated, with some slight differences, in rodent middens from the study area, in both paleowetland and rodent midden deposits north and south of the study area, and in lake level fluctuations on the adjacent Bolivian Altiplano. The regional synchroneity of these changes points to a strengthening of the South American Monsoon — which we term the “Central Andean Pluvial Event” — in two distinct intervals (15,900-13,800 and 12,700-9700 cal yr BP), probably induced by steepened SST gradients across the tropical Pacific (i.e., La Niña-like conditions).     

滇西南翁孔坝铜多金属矿床火山岩系地质特征及其与铜的成矿关系

翁孔坝铜多金属矿床是近年来在澜沧江构造带南段的云县-景洪火山弧上新发现的铜多金属矿床，与中三叠世陆相火山岩系密切相关，且具有较大的找矿潜力。文章在野外详细调查的基础上，结合赋矿火山岩岩石学特征，对矿区内火山岩系进行了系统研究，将其细分为5个喷发旋回，9个岩性段(T₂s^3-1～T₂s^3-9)，认为该矿床具有火山沉积-成岩成矿期和改造成矿期两期成矿作用，为陆相火山沉积-改造型铜多金属矿床。其中，火山岩成矿作用为成矿提供了物质来源，具有明显的岩性/岩相组合控矿特征，笔者综合认为该套火山岩系是矿床主要的控矿因素之一，进而初步建立了其与铜成矿的“时-空-成因”关系图。     

Alteration,mineralization, and genesis of the zoned Tongshan skarn-type copper deposit,Anhui, China

The Tongshan skarn-type copper deposit is located in the Anqing–Guichi ore cluster of the iron–copper metallogenic belt which occurs along the Middle–Lower Yangtze River Valley, China. In the study area, skarnization and mineralization took place along the contact zone between carbonates and granodiorite porphyries. The contact zone shows significant horizontal and vertical variations in alteration and mineralization. In the horizontal direction, the garnet content is high in the skarns near the intrusive body (proximal skarns), the diopside content is high farther from the intrusive body (distal skarns), and hedenbergite is concentrated in the skarns adjacent to the marble zone. Limestones located far from the marble zone experienced a strong silicification. In the vertical direction (from higher to lower levels), the rocks change from hornfels to calcareous skarn to magnesian skarn. Mineralogical studies show that the skarns near the intrusion are relatively oxidized, and the garnet in the skarns is relatively andradite rich. High concentrations of Cu are found in the porphyries with quartz veins, as well as in the calcic skarns, magnesian skarns, hornfelses, and marbles, which are located at distances of 13, 10, 43 and 25 m from the porphyries, respectively. High concentrations of Zn are found in silicified limestones and skarns located even farther from the porphyries. The present findings suggest that the Tongshan deposit was subjected to prograde alteration and mineralization, followed by retrogression. The alteration can be divided into a sequence of stages: contact metamorphism, prograde metasomatism, early retrogression, and late retrogression. The copper mineralization occurred mainly during the early retrogression, and the copper was further enriched in quartz veins within the porphyries during the late stages of magma evolution.     

云南羊拉铜矿床成矿流体特征及成矿过程

云南羊拉铜矿床位于金沙江构造带中部,是中-晚三叠世金沙江洋盆向西俯冲闭合碰撞造山过程中形成的一个大型铜矿床。矿体多呈层状、似层状顺层产出,但明显受层间破碎带和滑脱带控制。从流体包裹体研究入手,讨论了该矿床成矿流体的特征、演化以及流体不混溶(沸腾)作用与成矿的关系。流体包裹体研究表明,干夕卡岩阶段(Ⅰ)、湿夕卡岩磁铁矿阶段(Ⅱ)、石英硫化物阶段(Ⅲ)以及方解石硫化物阶段(Ⅳ)中发育多种类型的包裹体,主要为气液水两相包裹体和含子矿物多相包裹体,纯液相水包裹体次之,少见纯气相有机质包裹体。其中,含子矿物多相包裹体发育于Ⅰ阶段石榴石、Ⅱ阶段绿帘石,尤其是Ⅲ阶段石英中。Ⅰ、Ⅱ阶段成矿流体具有高温、高盐度特征,均一温度分别为413~593 ℃和336~498 ℃,盐度分别为19.1%~49.7% NaCleq和15.7%~53.3% NaCleq;Ⅲ阶段成矿流体均一温度为148~398 ℃,并具有低盐度(2.1%~9.6% NaCleq)与高盐度(35.5%~65.3% NaCleq)共存的特征;Ⅳ阶段成矿流体具有低温(132~179 ℃)、低盐度(3.4%~10.4% NaCleq)特征。根据流体包裹体的微观特征并结合矿区的宏观地质特征,认为流体不混溶(沸腾)是导致本矿区金属沉淀成矿的主要机制。     

Genesis of upper proterozoic stratabound copper mineralization,Kapunda, South Australia

Chalcopyrite-rich bedded and vein mineralization at Kapunda occurs in two locally developed dolosiltstone units within a sequence of generally darker-coloured, finer-grained calcmudstones and siltstones. The Mine Series accumulated in shallow water to supratidal, sabkha-like environments; there is no evidence for igneous activity in the region. Isotope data for bedded sulphides are characteristic of biological sulphate reduction in a restricted basin. It is likely that iron sulphides were produced initially, and that copper was introduced subsequently in mildly oxidizing, highly saline groundwaters, the influence of which is seen in the ¹³C-¹⁸O correlation for dolomite in the mineralized siltstones. Isotopic data support derivation of the veins from their host sediments, and this appears to have occurred before lithification.     

Paleoproductivity evolution off central Chile from the Last Glacial Maximum to the Early Holocene

A geochemical and paleontological reconstruction of paleoproductivity, upwelling intensity and sea surface temperature (SST) off central Chile at 35°S (GeoB3359-3) reveals marked changes from the Last Glacial Maximum (LGM) through the Early Holocene. Surface-water productivity was determined by the interaction between the atmospheric (the Southern Westerlies) and oceanographic (the Antarctic Circumpolar Current, ACC) systems from the LGM through early Termination I (TI). The northward shift of the climate zones during the LGM brought the ACC, as the main macronutrient source, closer to the GeoB3359-3, SST lowered, and surface water productivity and accumulation rates of biogenic components enhanced. With the poleward return of the Southern Westerlies and the ACC, the subtropical high-pressure system became the dominant atmospheric component southward till 35°S during the late TI and Early Holocene and caused surface water productivity to increase through enhanced upwelling.     

Mercury in Stratabound copper mineralization in the Mammoth area,northwest Queensland

Copper mineralization along the Mount Gordon Fault Zone in northwest Queensland contains sufficient mercury to permit mercury pathfinder techniques to be used for exploration for further deposits in the area. At the Mammoth mine, the No. 1 orebody contains 310–14000 ppb Hg, with the highest contents in “sooty chalcocite” which may be of supergene origin. The B orebody contains 100–4300 ppb Hg, with highest concentrations at the top of the deposit. Other deposits in the Mammoth area contain 10–1600 ppb Hg, with mean mercury contents > 200 ppb in fault-related mineralization.There is a strong positive correlation between mercury and copper, sulfur, silver, arsenic, bismuth, lead, antimony and thallium contents in the deposits which suggests mercury was introduced during the mineralizing process. However, most of the mercury occurs on the surfaces of sulfide minerals, indicating its introduction at a late stage of mineralization.Mercury in the No. 1 orebody is partly of supergene origin whereas primary mineralogy may control mercury distribution in the B orebody. The presence near the Mammoth Fault of a lens of pyrite containing high concentrations of mercury (geometric mean 820 ppb) suggests that the mercury content of pyrite encountered in future exploration programmes in the region might be used to indicate proximity to mineralized fault zones.Gossans derived from copper deposits contain more than five times the amount of mercury in ironstones developed over unmineralized or poorly mineralized fault zones. The mercury contents of iron-rich rocks may be used to discriminate gossans from the numerous fault ironstones in the Mammoth area.     

The partitioning of copper among selected phases of geologic media of two porphyry copper districts, Puerto Rico

In experiments designed to determine the manner in which copper is partitioned among selected phases that constitute geologic media, we have applied the five-step sequential extraction procedure of Chao and Theobald to the analysis of drill core, soils, and stream sediments of the Rio Vivi and Rio Tanama porphyry copper districts of Puerto Rico. The extraction procedure affords a convenient means of determining the trace-metal content of the following fractions: (1) Mn oxides and “reactive” Fe oxides; (2) “amorphous” Fe oxides; (3) “crystalline” Fe oxides; (4) sulfides and magnetite; and (5) silicates. An additional extraction between steps (1) and (2) was performed to determine organic-related copper in stream sediments.The experimental results indicate that apportionment of copper among phases constituting geologic media is a function of geochemical environment. Distinctive partitioning patterns were derived from the analysis of drill core from each of three geochemical zones: (a) the supergene zone of oxidation; (b) the supergene zone of enrichment; and (c) the hypogene zone; and similarly, from the analysis of; (d) soils on a weakly leached capping; (e) soils on a strongly leached capping; and (f) active stream sediment.The experimental results also show that geochemical contrasts (anomaly-to-background ratios) vary widely among the five fractions of each sampling medium investigated, and that at least one fraction of each medium provides substantially stronger contrast than does the bulk medium. Fraction (1) provides optimal contrast for stream sediments of the district; fraction (2) provides optimal contrast for soils on a weakly leached capping; fraction (3) provides optimal contrast for soils on a strongly leached capping.Selective extraction procedures appear to have important applications to the orientation and interpretive stages of geochemical exploration. Further investigation and testing of a similar nature are recommended.     

云南香格里拉春都斑岩铜矿区围岩蚀变及矿化特征

春都斑岩铜矿床地处著名的印支期中甸-义敦岛弧成矿带南端。矿区出露闪长玢岩-花岗闪长斑岩复式岩体,成矿岩体为印支晚期的花岗闪长斑岩。围绕成矿岩体,围岩蚀变强烈,蚀变分带明显,由中心向外,依次出现硅化钾化带→绢英岩化带→硅化带→硅化黑云母化带→青磐岩化带→绢云母化及泥化带。区内蚀变与矿化关系密切,蚀变类型决定矿化程度,蚀变...