山西省中条山铜矿田电气石与电气石岩的研究

本文通过对中条山铜矿田电气石和电气石岩地质产状、岩相学和矿物学、矿物化学等特征的研究，指出本区有三种成因类型的电气石：（１）北峪酸性侵入体岩浆期后热液成因电气石；（２）中条群地层中变质热液形成的电气石；（３）赋矿岩石和近矿围岩中热液蚀变电气石。第（３）类电气石具有特征的产状、矿物化学和矿物共生组合标型，是重要的找矿标志     

Geology,alteration and mesothermal Au-Ag-mineralization associated with a volcanic-intrusive complex at Mt. Shamrock-Mt. Ophir,SE Queensland

Au-Ag mineralization in the Mt-Shamrock — Mt. Ophir area of SE Queensland is related to a geographically-isolated calc-alkaline igneous centre consisting of high level plutonic and minor intrusions emplaced into the eroded remains of a silicic volcanic ediface and its basement. Mineralization occurs in both the igneous rocks and in the Permian siltstone country rocks and is controlled by a NE-trending structure parallel to Late Triassic lineaments. This structure is unrelated to, and younger than the exposed intrusions. Au-Ag-As-rich, Cu-Mo-poor mineralization occurs in breccias and veinlet networks within pervasively altered rocks characterized by silicification and H (sericite), CO₂ (calcite-ankerite), Na (albite), B (tourmaline), and S (pyrite) metasomatism. Secondary mineral compositions suggest that most of this alteration occurred at temperatures between 350 ° and 400 °C. The alteration was complex in detail and characterized by multiple hydrothermal events and space and/or time variations of physico-chemical conditions. Although some of these features are similar to prophyry deposits the chemical character of the alteration and mineralization is not typical of Cu-Mo-Au porphyries and has more in common with tectonometamorphic Au deposits formed at considerably greater depths.     

浙闽地区叶蜡石矿床成矿规律研究

叶蜡石矿床是一种重要的非金属矿产,主要分布于东南沿海地区侏罗纪—白垩纪的中酸性火山岩地层中,受控于区域大规模断裂和伸展断陷盆地。文章对中国内外叶蜡石矿床的地质和矿产特征进行了综合分析,总结了浙闽地区叶蜡石矿床特征和成因。浙闽地区叶蜡石矿床的赋矿原岩为流纹质火山碎屑岩和凝灰岩等,具有高硅高铝的特点。矿床成因类型主要包括火山热液交代型和火山热液充填型。结合泰顺龟湖、青田周村和山口等典型叶蜡石矿床的实例研究,文章揭示了火山热液交代型叶蜡石矿床普遍发育硅化、叶蜡石化、明矾石化、黄铁矿化的垂直分带特征,中酸性火山岩组分在热液作用下发生交代、分解,使铝有规律的富集成矿;火山热液充填型叶蜡石矿床围岩蚀变分带不明显,从围岩中淋滤、萃取的硅铝组分沿着构造裂隙运移,在有利的空间成矿。因此,笔者认为侏罗纪—白垩纪中酸性火山岩与凝灰岩、区域断裂带和火山岩带、围岩蚀变垂直分带以及陡峭山峰是叶蜡石矿的重要找矿标志。     

From intrusion-related to orogenic mineralization: The Wasamac deposit,Abitibi Greenstone Belt,Canada

The Wasamac deposit is an example of Archean greenstone-hosted gold deposit located in the Abitibi Belt, 15 km southwest of Rouyn-Noranda. The deposit is hosted by a second-order ductile shear zone of the Cadillac–Larder Lake Fault Zone (CLLFZ), known as the Francoeur-Wasa Shear Zone (FWSZ). It regionally sits at the boundary between the orogenic gold district of Noranda and the Kirkland Lake gold district dominated by intrusion-related gold systems. This specific location in-between two different gold mineralization environments sets the Wasamac deposit apart as a prime candidate for investigating hydrothermal processes along the CLLFZ. Within the Wasamac deposit, gold distribution is constrained to the altered mylonitized portion of the FWSZ; lode systems are absent. Hydrothermal alteration and associated disseminated mineralization occurs as a replacement of the Blake River Group metavolcanic units. The hydrothermal signature displays two distinct alkaline alteration assemblages: potassic and albitic, each associated with specific gold characteristics. (1) Potassic alteration is characterized by the crystallization of microcline, carbonates and quartz. Within this assemblage gold is associated with porous pyrite enriched in Te-Ag-Au-Mo-Pb-Bi-W, deposited under oxidizing conditions. Such characteristics are widely described in the Kirkland Lake area, and are found in examples of syenite-related mineralization, such as the Beattie and Malartic gold deposits. (2) The albitic alteration assemblage, composed of albite, sericite and carbonates, reflects more reduced hydrothermal conditions with mineralization characterized by free native gold. This hydrothermal event is coeval with the brecciation of early gold-rich pyrite reflecting a structural overprint that controlled late-stage gold characteristics. These alteration and structural features are common in orogenic gold deposits both worldwide and regionally, particularly at the neighbouring Kerr-Addison and Francoeur deposits, and in lode-gold systems such as in the Sigma-Lamaque deposit.The gold mineralization at Wasamac has similar characteristics to both intrusion-related gold systems and structurally controlled orogenic gold deposits. Hydrothermal and structural crosscutting relationships at Wasamac indicate that a structurally controlled hydrothermal event overprinted earlier potassic magmatic-hydrothermal alteration. This observation supports a multistage process of gold concentration during which new gold characteristics, metal anomalies, fluid conditions and alteration assemblages replaced earlier stages of gold enrichment, in places completely obliterating previous signatures. We propose that the Wasamac deposit was originally related to an alkaline intrusion buried at depth beneath the Francoeur-Wasa Shear Zone.     

Hydrothermal Alteration of the Saplica Volcanic Rocks,Sebinkarahisar, Turkey

A widespread, intense hydrothermal alteration zone has developed in the Cretaceous Saplica volcanics as a result of the intrusion of Late Cretaceous-Paleocene granitoids. The propylitic, phyllitic (sericitic), and argillic alteration along with hematite, silica polymorphs, and two types of tourmaline mineralization developed under a wide range of Eh and pH conditions.

Alunite, kaolinite, and silica are abundant in the argillic alteration, whereas sericite dominates in the phyllic alteration. Most of the major alunite deposits are located along the periphery of the Saplica volcanic rocks and in addition contain alunite, kaolinite + quartz ± opal ± cristobalite. Illite and pyrite, barite, and gypsum also occur in small amounts.

Major and trace elements are concentrated in, or were leached from, the volcanic rocks, depending upon the alteration types. In general, Al + K and Mg + Ca + Fe were enriched in the alunitic + sericitic and propylitic alteration types, respectively. On the other hand, Ca, Mg, and Fe were leached during argillic alteration, and Fe was concentrated in hematite formation. Strong leaching of Na was determined for alteration types. Silica generally decreased in argillitic (kaolinitic and alunitic) alteration zones. Most trace elements were mobile during hydrothermal alteration. Y, Sc, Mo, Cr, Co, Ni, and Zn tend to be mobile in acid aqueous systems, and thus are nearly absent in these alunitic alteration zones. In the surrounding kaolinitic envelope, these elements are present at background (average) or slightly higher concentrations. Rb and Sr contents are high in the alunitic and kaolinitic zones. Barium is highest near the alunite zone because of the relative insolubility of barite in acidic solutions. Pb and Cu contents increase in the propylitic zone. Such hydrothermal alteration zones can be used effectively in the exploration and evaluation of mineral resources of the eastern Black Sea region.     

Geology and Hydrothermal Alteration of the Duobuza Gold‐Rich Porphyry Copper District in the Bangongco Metallogenetic Belt,Northwestern Tibet

The Duobuza gold‐rich porphyry copper district is located in the Bangongco metallogenetic belt in the Bangongco‐Nujiang suture zone south of the Qiangtang terrane. Two main gold‐rich porphyry copper deposits (Duobuza and Bolong) and an occurrence (135 Line) were discovered in the district. The porphyry‐type mineralization is associated with three Early Cretaceous ore‐bearing granodiorite porphyries at Duobuza, 135 Line and Bolong, and is hosted by volcanic and sedimentary rocks of the Middle Jurassic Yanshiping Formation and intermediate‐acidic volcanic rocks of the Early Cretaceous Meiriqie Group. Simultaneous emplacement and isometric distribution of three ore‐forming porphyries is explained as multi‐centered mineralization generated from the same magma chamber. Intense hydrothermal alteration occurs in the porphyries and at the contact zone with wall rocks. Four main hypogene alteration zones are distinguished at Duobuza. Early‐stage alteration is dominated by potassic alteration with extensive secondary biotite, K‐feldspar and magnetite. The alteration zone includes dense magnetite and quartz‐magnetite veinlets, in which Cu‐Fe‐bearing sulfides are present. Propylitic alteration occurs in the host basic volcanic rocks. Extensive chloritization‐silicification with quartz‐chalcopyrite or quartz‐molybdenite veinlets superimposes on the potassic alteration. Final‐stage argillic alteration overlaps on all the earlier alteration. This alteration stage is characterized by destruction of feldspar to form illite, dickite and kaolinite, with accompanying veinlets of quartz + chalcopyrite + pyrite and quartz + pyrite assemblages. Cu coexists with Au, which indicates their simultaneous precipitation. Mass balance calculations show that ore‐forming elements are strongly enriched during the above‐mentioned three alteration stages.     

Geology,alteration, age,and origin of iron oxide–apatite deposits in Upper Eocene quartz monzonite,Zanjan district,NW Iran

Iron oxide–apatite deposits are present in Upper Eocene pyroxene-quartz monzonitic rocks of the Zanjan district, northwestern Iran. Mineralization occurred in five stages: (1) deposition of disseminated magnetite and apatite in the host rock; (2) mineralization of massive and banded magnetite ores in veins and stockwork associated with minor brecciation and calcic alteration of host rocks; (3) deposition of sulfide ores together with potassic alteration; (4) formation of quartz and carbonate veins and sericite, chlorite, epidote, silica, carbonate, and tourmaline alteration; and (5) supergene alteration and weathering. U–Pb dating of monazite inclusions in the apatite indicates an age of 39.99?±?0.24 Ma, which is nearly coeval with the time of emplacement of the host quartz monzonite, supporting the genetic connection. Fluid inclusions in the apatite have homogenization temperatures of about 300 °C and oxygen isotopic compositions of the magnetite support precipitation from magmatic fluids. Late-stage quartz resulted from the introduction of a cooler, less saline, and isotopically depleted fluid. The iron oxide–apatite deposits in the Tarom area of the Zanjan district are typical of a magmatic–hydrothermal origin and are similar to the Kiruna-type deposits with respect to mineral assemblages, fabric and structure of the iron ores, occurrence of the ore bodies, and wall rock alteration.     

Tourmalinization related to Late Proterozoic-Early Palaeozoic lode gold mineralization in the Bin Yauri area, Nigeria

Three types of tourmaline occurrence have been identified in the area of Bin Yauri, Nigeria, mesothermal lode-gold mineralization. These are: (1) stratabound tourmalinites in pelitic metasediments, (2) tourmaline in a hydrothermal alteration assemblage within hornfelsed wall rocks, (3) tourmaline in auriferous quartz and quartz-carbonate veins. Although the tourmaline occurrences are all within or close to the contact aureole of a granodiorite intrusion, geochemical characteristics of the tourmalines are broadly similar and reflect a common metasedimentary source. Two stages of tourmalinization are envisaged. The earlier (ca. 1100 Ma) involved syngenetic-diagenetic formation of tourmalinites, while the later (ca. 500 Ma) involved epigenetic (hydrothermal) tourmaline-gold mineralization, possibly derived by dehydration and devolatilization of metasedimentary sequences containing tourmaline-rich rocks or tourmalinites. Electron microprobe analyses indicate that the tourmalines are intermediate members of the schorl-dravite solid solution series. Plots involving FeO, MgO, and/or Al₂O₃ from these analyses are used to constrain the sources and processes of tourmalinization. Two metallogenic implications are derived from this study. One is that, although the tourmalinites are barren of gold and base metal mineralization, their occurrences nevertheless encourages exploration for syngenetic-exhalative massive sulphide deposits in the region. The other implication applies to the potential use of tourmaline in deciphering the physico-chemical conditions of gold-mineralizing fluids in the Bin Yauri area.     

Hydrothermal alteration and magnetic properties of rocks in the Carolina de Michilla stratabound copper district,northern Chile

In the Carolina de Michilla district, northern Chile, stratabound copper mineralization is hosted by Jurassic volcanic rocks along the trace of the Atacama fault system. In this study, we present the overall effects of hydrothermal alteration on the magnetic properties of rocks in this district. Two types of metasomatic alteration associations occur, one of regional extent and the other of local hydrothermal alteration associated with copper mineralization (e.g., Lince–Estefanía–Susana). Regional alteration is interpreted as a low-grade “propylitic association” characterized by an epidote–chlorite–smectite–titanite–albite–quartz–calcite association. The local hydrothermal alteration is characterized broadly by a quartz–albite–epidote–chlorite–calcite mineral assemblage. The most pervasive alteration mineral is albite, followed by epidote and, locally, actinolite. These minerals contrast sharply against host rock minerals such as chlorite, calcite, zeolite, prehnite, and pumpellyite, but alteration is constrained to mineralized bodies as narrow and low contrast alteration halos that go outwards from actinolite–albite to epidote–albite, to epidote–chlorite, and finally to chlorite. Hydrothermal alteration minerals, compared to regional alteration minerals, show iron-rich epidotes, a lower chlorite content of the chlorite–smectite series, and a nearly total albite replacement of plagioclase in the mineralized zones. Opaque minerals associated with regional alteration are magnetite and maghemite, and those associated to hydrothermal alteration are magnetite, hematite, and copper sulphides. We present paleomagnetic results from nine sites in the Michilla district and from drill cores from two mines. Local effects of hydrothermal alteration on the original magnetic mineralogy indicate similar characteristics and mineralogy, except for an increase of hematite that is spatially associated with the Cu–sulphide breccias with low magnetic susceptibilities. Results indicate that it is impossible to magnetically differentiate mineralized bodies from unmineralized lavas, except for pyrite-rich hydrothermal breccias. In conclusion, for stratabound copper deposits of the Michilla type, the overall effect of hydrothermal alteration on the paleomagnetic properties of rocks is of low contrast, not clearly discernable even at a small scale. From an exploration point of view, magnetic exploration surveys should not discern mineralized bodies of Cu–sulphide breccias except in detailed ground surveys due to the small size of contrasting bodies. Unoriented drill cores with primary ore mineralization record a characteristic remanent magnetization of reverse polarity. Taking into account the azimuth and dip of the drill cores, we were able to compare the magnetization of the mineralized bodies with the characteristic directions from sites drilled in situ from Late Jurassic–Early Cretaceous intrusives mostly. The characteristic direction recorded by the Pluton Viera is similar to the magnetization of the ore bodies of the Estefania mine. If copper mineralization mostly postdates the tilt of the volcanic flows, the low paleomagnetic inclinations suggest an age for the mineralization near 145 Ma, the time of the lowest paleolatitude for the South American plate during the Mesozoic.     

甘肃白银折腰山型和石青硐型块状硫化物矿床综合信息找矿模型研究

甘肃白银厂-石青硐火山岩带是北祁连地区块状硫化物矿床成矿带的主要地段，在其中已发现6个工业矿床。典型矿床的综合信息找矿模型研究对于进一步开展矿体定位预测具有重要意义。文章将已发现的矿床划分为火山喷口Cu(Zn)型(折腰山型)、火山喷口斜坡Zn—Pb-Cu型(小铁山型)和火山沉积洼地Pb-Zn-Cu型(石青硐型)三(亚)类，并通过对典型矿床的地质特征、地球物理特征、地球化学特征及找矿标志等进行对比分析和研究，建立了折腰山型、石青硐型两类矿床的综合信息找矿模型。应用该模型在黑石山地区进行成矿预测，取得了良好的效果。     

电气石——成岩成矿作用的灵敏示踪剂

本文详细论述了电气石的化学组成（主化学元素、微量元素和稀土元素）和同位素组成Ｈ、Ｏ、Ｂ、Ｓｉ、Ｒｂ／Ｓｒ、Ｓｍ／Ｎｄ、ｐｂ／ｐｂ和Ｋ／Ａｒ）特征,提出电气石可以作为研究成岩成矿作用的一个灵敏示踪剂。利用电气石的主化学元素和微量、稀土元素组成,可以有效指示其形成的物理化学环境,还可以作为一种有用的找矿标志,指标矿化的存在,并可能用于区分矿化类型和矿体规模。电气石的稳定同位素和放射性同位素研究,已经用     

Geological and Geochemical Characteristics of the Hydrothermal Clay Alteration in South Korea

Abstract: Hydrothermally altered areas forming pyrophyllite‐kaolin‐sericite‐alunite deposits are distributed in Chonnam and Kyongsang areas, Cretaceous volcanic field of the Yuchon Group. The Chonnam alteration area is located within depression zone which is composed of volcanic and granitic rocks of late Cretaceous age. The clay deposits of this area show the genetic relationship with silicic lava domes. The Kyongsang alteration area is mainly distributed within Kyongsang Basin comprising volcanic, sedimentary and granitic rocks of Cretaceous and Tertiary age. Most of the clay deposits of this area are closely related to cauldrons. Paleozoic clay deposit occurs in the contact zone between Precambrian Hongjesa granite gneiss and Paleozoic Jangsan quartzite of Choson Supergroup. Cretaceous igneous rocks of the both alteration areas belong to high K calc‐alkaline series formed in the volcanic arc of continental margin by subduction‐related magmatism. Chonnam igneous rocks show more enrichment of crustal components such as K, La, Ce, Sm, Nd and Ba, higher (La/Yb)cn ratio, and higher initial ⁸⁷Sr/⁸⁶Sr ratio (0. 708 to 0. 712) than those of Kyongsang igneous rocks. This might be due to the difference of degree of crustal contamination during Cretaceous magmatism. The most characteristic alteration minerals of Chonnam clay deposits are alunite, kaolin, quartz, pyrophyllite and diaspore which were formed by acidic solution. Those of Kyongsang clay deposits are sericite, quartz and pyrophyllite which were formed by weak acid and neutral solution. The formation ages of the clay deposits of two alteration areas range from 70. 1 to 81. 4 Ma and 39. 7 to 79. 4 Ma, respectively. The Daehyun clay deposit in Ponghwa area of Kyongsang province shows the alteration age range from 290 to 336 Ma. This result shows the different alteration episode from the hydrothermal alteration of Cretaceous to early Tertiary in the Kyongsang and Chonnam alteration areas. These data indicate, at least, three hydrothermal activities of Tertiary (middle to late Eocene), late Cretaceous (Santonian to Maastrichtian) and Paleozoic Carboniferous Periods in South Korea.     

中国东部冰长石—绢云母型低温浅成热液金矿

中国东部许多金矿床产在中生代火山岩中,前人将其归于火山热液型矿床,作者将其划为冰长石-绢云母型低温浅成热液矿床,并讨论了其主要特征.许多产在变质岩和花岗岩中金矿过去分别归于变质热液和岩浆热液或者统称中温或中低温热液矿床,其中一部分作者也将其归于冰长石-绢云母型低温浅成热液矿床.这种矿床斑岩型金矿在空间上叠加,在国外有例子,在国内虽有争议,但有可能存在.文中讨论了美洲西部太平洋岛弧与中国东部矿床类型组合类似,但成矿时代有所差别,并从板块构造角度对比进行解释.作者强调指出,由于我国东部成矿时代老,剥蚀作用使得我们对这种矿床认识产生困难,但只要努力一定能打开找矿新思路.     

Regional-scale hydrothermal alteration in the Central Blake River Group,western Abitibi subprovince,Canada: implications for VMS prospectivity

The Late Archean Blake River Group is a thick succession of predominantly mafic volcanic rocks within the southern zone of the Abitibi greenstone belt. It contains a number of silicic volcanic centers of different size, including the large Noranda volcanic complex, which is host to 17 past-producing volcanogenic massive sulfide deposits. The Noranda complex consists of a 7- to 9-km-thick succession of bimodal mafic and felsic volcanic rocks erupted during five major cycles of volcanism. Massive sulfide formation coincided with a period of intense magmatic activity (cycle III) and the formation of the Noranda cauldron. Hydrothermal alteration in these rocks is interpreted to reflect large-scale hydrothermal fluid flow associated with rapid crustal extension and rifting of the volcanic complex. The alteration includes abundant albite, chlorite, epidote and quartz (silicification), which exhibit broad stratigraphic and structural control and correlate with previously mapped whole-rock oxygen isotope zonation. The Mine Sequence volcanic rocks are characterized by abundant iron-rich chlorite (Fe/Fe+Mg >0.5), hydrothermal amphibole (ferroactinolite) and coarse-grained epidote of clinozoisite composition (<10 wt% Fe ₂O ₃). Volcanic rocks of the pre-cauldron sequences, which contain only subeconomic stringer mineralization, are characterized by less abundant chlorite and mainly fine-grained epidote (>10 wt% Fe ₂O ₃) lacking the clinozoisite solid solution. Alteration in the Mine Sequence volcanic rocks persists along strike well beyond the limits of the main ore deposits (as far as several tens of kilometers) and can be readily distinguished from greenschist facies metamorphic assemblages at a regional scale. The lack of similar alteration in the pre-cauldron sequences is consistent with limited ¹⁸O-depletion and suggests that the early history of the volcanic complex did not support large-scale, high-temperature fluid flow in these rocks. Comparisons with a much smaller, barren volcanic complex in nearby Ben Nevis township reveal important differences in the alteration mineralogy between volcanoes of different size, with implications for area selection during regional-scale mineral exploration. The Ben Nevis Complex consists of a 3- to 4-km-thick succession of mafic, intermediate and felsic volcanic rocks centered on a small subvolcanic intrusion. Alteration of the volcanic rocks comprises mainly low-temperature assemblages of prehnite, pumpellyite, magnesium-rich chlorite (Fe/Fe+Mg <0.5), iron-rich epidote (>10 wt% Fe ₂O ₃) and calcite. Actinolite ± magnetite alteration occurs proximal to the intrusive core of the complex, but the limited extent of this alteration indicates only local high-temperature fluid circulation adjacent to the intrusion. A distal zone of carbonate alteration is located 4–6 km from the center of the volcano. Although iron-bearing carbonates are present locally within this zone, the absence of siderite argues against a high-temperature origin for this alteration. These observations do not offer positive encouragement for the existence of a fossil geothermal system of sufficient size or intensity to have produced a large massive sulfide deposit.     

祁连山中段托勒山地区奥陶纪火山岩岩金矿床控矿因素分析

[摘 要] 祁连山中段托勒山岩金多分布在奥陶纪火山岩地层内,地层控矿特征十分明显。区内与火山活动有关的成矿作用主要是火山喷发后期火山热液形成的热液型矿床,其次是后期岩浆活动提供热源和大量的岩浆热液交代、充填形成中低温热液矿床和接触蚀变型矿床。从找矿前景上来看,本区虽然金矿点、矿化点分布较多,但少有规模较大的矿床。因此本区找矿上应该以寻找火山热液蚀变型矿产为主。     

Mixed messages in iron oxide–copper–gold systems of the Cloncurry district,Australia: insights from PIXE analysis of halogens and copper in fluid inclusions

Proterozoic rocks of the Cloncurry district in NW Queensland, Australia, are host to giant (tens to hundreds of square kilometers) hydrothermal systems that include (1) barren regional sodic–calcic alteration, (2) granite-hosted hydrothermal complexes with magmatic–hydrothermal transition features, and (3) iron oxide–copper–gold (IOCG) deposits. Fluid inclusion microthermometry and proton-induced X-ray emission (PIXE) show that IOCG deposits and the granite-hosted hydrothermal complexes contain abundant high temperature, ultrasaline, complex multisolid (type 1) inclusions that are less common in the regional sodic–calcic alteration. The latter is characterized by lower salinity three-phase halite-bearing (type 2) and two-phase (type 3) aqueous inclusions. Copper contents of the type 1 inclusions (>300 ppm) is higher than in type 2 and 3 inclusions (<300 ppm), and the highest copper concentrations (>1,000 ppm) are found both in the granite-hosted systems and in inclusions with Br/Cl ratios that are consistent with a magmatic source. The Br/Cl ratios of the inclusions with lower Cu contents are consistent with an evaporite-related origin. Wide ranges in salinity and homogenization temperatures for fluid inclusions in IOCG deposits and evidence for multiple fluid sources, as suggested by halogen ratios, indicate fluid mixing as an important process in IOCG genesis. The data support both leaching of Cu by voluminous nonmagmatic fluids from crustal rocks, as well as the direct exsolution of Cu-rich fluids from magmas. However, larger IOCG deposits may form from magmatic-derived fluids based on their higher Cu content.     

Hydrothermal alteration of felsic volcanic rocks associated with massive sulphide deposition in the northern Iberian Pyrite Belt (SW Spain)

Massive sulphide deposits of the northern Iberian Pyrite Belt (IPB) are mainly hosted by felsic volcanic rocks of rhyolitic to dacitic composition. Beneath most of the massive ores of this area (e.g., Concepción, San Miguel, Aguas Teñidas Este or San Telmo deposits) there is usually a wide hydrothermal alteration halo associated with stockwork-type mineralization. Within these alteration envelopes there are two principal rock types: (1) chlorite-rich rocks, linked to the inner and more intensely altered zones and dominantly comprising chlorite+pyrite+quartz+sericite (+carbonate+rutile+zircon+chalcopyrite), and (2) sericite-rich rocks, more common in the peripheral zones and showing a dominant paragenesis of sericite+quartz+pyrite+chlorite (+carbonate+rutile+zircon+sphalerite). Mass-balance calculations comparing altered and least-altered felsic volcanic rocks suggest that sericitization was accompanied by moderate enrichment in Mg, Fe and H₂O, with depletion in Si, Na and K, and a slight net mass loss of about 3%. Chloritization shows an overall pattern which is similar to that of the sericitic alteration, but with large gains in Fe, Mg and H₂O (and minor enrichment in Si, S and Mn), and a significant loss of Na and K and a minor loss of Ca and Rb. However, chloritization has involved a much larger net mass change (mass gain of about 28%). Only a few elements such as Nb, Y, Zr, Ti, P and LREE appear to have remained inert during hydrothermal alteration, whilst Ti and Al have undergone very minor mobilization. The results point to the severity of the physico-chemical conditions that prevailed during the waxing stage of the ore-forming hydrothermal systems. Further, mineralogical and geochemical studies of the altered footwall rocks in the studied deposits indicate that hydrothermal ore-bearing fluids reacted with host rocks in a multi-stage process which produced a succession of mineralogical and chemical changes as the temperature increased.     

Implications of Pb isotope signatures of rocks and iron oxide Cu-Au ores in the Candelaria-Punta del Cobre district,Chile

Lead isotope ratios of ores of the Candelaria-Punta del Cobre iron oxide Cu-Au deposits and associated Early Cretaceous volcanic and batholithic rocks have been determined. For the igneous rocks, a whole-rock acid attack technique based on the separate analyses of a leachate and the residual fraction of a sample was used. The lead isotope systematics of leachate–residue pairs are significantly different for unaltered and altered igneous rocks of the Candelaria-Punta del Cobre district. Residues of unaltered igneous rocks likely represent the common lead. In contrast, residues of all the altered igneous rocks except two samples have higher Pb isotope ratios than those of unaltered magmatic rocks and cannot represent common lead. We suggest that this is a result of the hydrothermal alteration suffered by these rocks and that the common lead composition of the altered igneous (volcanic and plutonic) rocks must have been similar to that of the unaltered batholith rocks. The conclusion that the altered volcanic rocks originally had a similar common lead isotope composition as the batholith is consistent with geological and geochemical arguments (e.g., setting, regional geologic evolution, ages and relative distribution of volcanic and intrusive rocks, magmatic affinities), which indicate that these rocks were derived from similar Early Cretaceous parent magmas. The modification of the leachate–residue pair lead isotope systematics of most altered igneous rocks is consistent with a selective removal of lead and uranium from these rocks by an oxidized hydrothermal fluid. The result of the hydrothermal leaching has been to alter magmatic rocks in a way that (1) their leachable fraction is presently a mix of common lead similar to that of the ore event and of radiogenic lead evolved from a source with a consistently high Th/U, and that (2) their residual fraction has less common lead than unaltered rocks. The outcrop area with altered volcanic rocks displaying anomalously high lead isotope ratios extends over 25 km along the eastern margin of the batholith. Since lead of the ores in the Candelaria-Punta del Cobre district has the same isotopic composition as the common lead of unaltered magmatic rocks of the area, the lead isotope data are consistent with a derivation of the ore lead (and by inference of other metals like Cu) both directly from a magmatic fluid exsolved during crystallization of the batholith and/or from hydrothermal leaching of the volcanic rocks originally having similar isotopic compositions as the batholith.Editorial handling: B. Lehmann     

Mineral Chemistry and Boron Isotopic Composition of Tourmaline from the Devonian Metallogenic District of Shanyang-Zhashui,Eastern Qinling

Toumaline is widespread in the host strata of strata-bound base metal sulphide deposits in the Devonian metallogenic district around Shanyang-Zhashui in eastern Qinling. As a member of the schorl-dravite series, the tourmaline is characterized by Mg > Fe and Na > Ca, showing apparent chemical zonation which records the geochemistry during its formation and subsequent regional metamorphism and hydrothermal overprint. The close similarity in chemical and isotopic constitutions between the tourmaline of the main metallogenic epoch in this district [FeO/(FeO + MgO)=0.34 − 0.39 and δ¹¹B=−7.6‰ − − 8.8‰] and those related to massive sulphide deposits typical of submarine (exhalative) hydrothermal sedimentation may add further support to a similar mechanism of mineralization for the strata-bound deposits in the district. Supported by the Foundation for Young Scientists under the National Natural Science Foundation of China.     

北祁连山中西段塞浦路斯型铜矿特征、成矿作用及找矿标志

本文总结北祁连山中西段塞浦路斯型铜矿特征及找矿标志 ,获得如下认识 :1成矿环境为奥陶纪亲弧扩张脊 (岛弧扩张脊和弧后扩张脊 ) ,容矿岩石为蛇绿岩套上部火山 -沉积岩系 ;矿床成矿金属组合为铜锌 ,贫铅 ;2矿床地质模型为蘑菇状 ,蘑菇茎代表沿热液通道的柱状矿体 ,蘑菇伞代表在热液喷流口周围海底展开的透镜状、似层状矿体 ,伞翼之下为基性火山岩 ,伞上常覆盖碧玉岩 ,成矿环境不稳定时 ,缺失碧玉岩。近喷流口位置矿体 Cu>Zn,远喷流口位置矿体 Cu相似文献