Metalliferous Mineralization Research Articles

Mineralización de afinidad granítica en la porción central del batolito de Colangüil. Provincia de San Juan, Argentina

The central portion of the Batholith of Colangüil belongs to the Frontal Range and is located in the northwest of San Juan province, Argentina. It includes different granite units of Permian in age: Romo, Conconta, and Agua Blanca. These intrude the Cerro Agua Negra Formation, an Upper Carboniferous - Asselian sedimentary unit. These units are partially covered by volcaniclastic rocks of the Choiyoi Group, lower Permian-Triassic in age. The region was characterized by mineral extractions during the last century. Metalliferous mineralization has been recognized in the higher elevation areas of the Conconta and Agua Blanca plutons, with an early paragenesis of wolframite, fluorite, niobium, and quartz, and later deposition of scheelite, in quartz gangue. The latter was observed in the Agua Blanca pluton. The tectonic of the Cisuralian Permian San Rafael phase, compressive in nature, affected mainly the Cerro Agua Negra Formation. An oriented NW-SE fault array on the aforementioned igneous and sedimentary units stands out. Two regional fracturing axes limit laterally this sector of the batholith and match the location of the mineral deposits. A greater ascent of granite basement blocks can be seen to the south of the Conconta pluton and in the surroundings of the Agua Blanca pluton, based both on the intense erosion of its sedimentary host rock and by the little development of mineralization in the Romo sector. The fluid inclusion assemblages present in the veins of the Conconta and Romo sectors are linked with saline and carbonic fluid types, typical of the tungsten deposition cycle.

A Review of the Metalliferous Mineralization of the Lower Paleozoic Fiambalá Mafic-Ultramafic Complex, Argentina

A Review of the Metalliferous Mineralization of the Lower Paleozoic Fiambalá Mafic-Ultramafic Complex, Argentina

Identification of hydrothermal paleofluid pathways, the pathfinders in the exploration of mineral deposits: A case study from the Sukumaland Greenstone Belt, Lake Victoria Gold Field, Tanzania

Hydrothermal fluids play a key role in the process of metalliferous mineralization such as gold deposits. The modern exploration indicators for such deposits are tectonic structures and characteristic alteration minerals observed as detectable halos adjacent to mineral deposits. Tectonic fractures are the conduits to these hydrothermal fluids and thus control the spatial locations for the formation of mineral deposits. Along crustal structures, hydrothermal fluids commonly induce mineral alteration in the adjacent wall rocks depending on the physical–chemical conditions. These alteration patterns, which are the pathfinders for the proxies in the modern mineral exploration, can be detected by innovative application of combined remote sensing techniques. The study area has experienced intense tectonic deformations, which resulted to two major sets of structures, the NW–SE and NE–SW-trending structures. The knowledge-based analysis applied to SRTM data was useful in identifying crustal lineaments, which the above two set of structures, truncating lithological units of the Sukumaland Greenstone Belt were identified. The Feature Oriented Principal Component Selection (FPCS) together with the GIS functions applied to Landsat 7ETM+ data, were useful to enhance signals from hydrothermal alteration minerals. Results have revealed that the Sukumaland Greenstone Belt is intensively fractured, in a systematic pattern, and has apparently been “injected” with large volumes of hydrothermal fluids. Both processes together have resulted in the systematic and structurally controlled hydrothermal alteration patterns. In this study linear alteration patches are interpreted to represent the hydrothermal paleofluid pathways. Alteration patches coincide spatially with regional and local tectonic structures and are consistent with major gold occurrences and gold mines. This study indicate that careful analysis of SRTM and Landsat ETM+ data can identify crustal lineaments, the likely hydrothermal paleofluid conduits, which may lead to the discovery of potential ore deposits.

Chemical and mineralogical data of the metalliferous mineralization from S. Carlo mine (Peloritani mts, Ne Sicily, Italy)

The mineralization processes in the Peloritani Belt (Southern Sector of the Calabria- Peloritani Arc) prevalently developed during the Variscan orogenesis producing Pb, Zn, Fe, As, Sb, Cu, Ag, W, etc. polymetalliferous ore-bearing horizons. This paper focuses on the polymetalliferous mineralization recognised in the ancient S. Carlo Mine, which has already been subject of some studies and is part of an important discordant vein deposits system that are widespread in the Mandanici Unit (MaU). This Unit is characterized by a Variscan low-P, polyphasic and plurifacial metamorphic basement, exhibiting a prograde zoning, from chlorite zone of greenschist facies to oligoclase-almandine zone of amphibolite facies. The Variscan main foliation (Fv2) is irregularly cut by mineralized veins of decimetric to metric width. They are also perpendicular to the Alpine mylonitic shear zones of metric thickness developing along the sub-horizontal tectonic contacts between the tectono-stratigraphic units. These vein deposits formed along late-Alpine systems of fractures and faults, after Peloritani nappe emplacement. Minerographic study reveals a metalliferous mineral association mainly composed of tetrahedrite associated with, in order of decreasing abundance, chalcopyrite, bournonite, pentlandite, stromeyerite, arsenopyrite, scheelite, galena, sphalerite, pyrite, bismuthinite, boulangerite, jamesonite, covellite, bornite and argentite. Quartz, siderite and ankerite among non-metalliferous minerals are predominant. This work has been supported by mineralogical studies and chemical analyses carried out by Atomic Absorption and Inductively Coupled Plasma-Mass Spectrometry on powdered and separated samples of minerals. Geochemical data (major and trace elements) have allowed a detailed characterization of the minerals. They have revealed that the most significant minerals with Au contents around 1 ppm are tetrahedrite, sphalerite, chalcopyrite and bournonite. The presence of this noble metal in all minerals is important and shows that the mineralizing event is late and widespread. The Ag content is generally about 2000 ppm in all metalliferous minerals, and is higher than those found in the same minerals of other Peloritani deposits in which this content is around 1000 ppm. Sphalerite and carbonates show very low Ag content. Chalcopyrite, sphalerite, bournonite and tetrahedrite show high contents of Ni, As, Bi. Cd and Mn are concentrated in sphalerite. Fe content in sphalerite is on average > 6%, in agreement with pressure-temperature conditions (pressure from 2 to 3 kbar and temperature from 420 to 550 C).

Regional geochemistry, terrane analysis and metallogeny in the British Caledonides

Abstract The Caledonides of northern Britain are commonly divided into an assemblage of terranes based on the interpretation of geology in relation to major fault structures. This paper incorporates metallogenic concepts into the terrane model and uses systematic regional geochemical data to constrain models of terrane configuration and evolution: analyses of one-, two- and three-component geochemical images are used to identify changes in the levels of single elements and their ratios across the orogen. The distribution of sedimentary exhalative (SEDEX) ore deposits and volcanogenic massive sulphide, and mesothermal and epithermal gold mineralization is shown to reflect the presence of long-lived metallogenic provinces which have distinctive geochemistry reflecting their origin as zones of crustal extension and lithospheric thinning. The geochemistry of the northern Caledonides reflects the predominantly lower crustal nature of the Laurentian continental margin, now exposed in the Lewisian foreland and Caledonized Lewisian inliers in the Moine succession. In contrast, the Avalonian Plate has a more evolved geochemistry, although the ratios of elements associated with basic rocks suggests that they were less fractionated during emplacement into the thinner crust of Avalonia and the Iapetus Suture Zone. The predominantly psammitic Moine Supergroup and the Grampian Group Dalradian have an evolved chemistry consistent with derivation from a higher crustal level than that of the exposed Lewisian complex; basin-scale variations, such as the proportion and composition of arkosic material, are also evident. The regional pattern was intermittently disrupted by the influx of mantle material during deposition of the mineralized Argyll and Southern Highland groups (Dalradian), and later as intrusions were emplaced from early Ordovician (Grampian Orogeny) to early Devonian times. South of the Southern Upland Fault, the geochemical patterns suggest a complex interplay of sedimentary provenance and depositional environments during the final stages of collision between Laurentia and Avalonia. Provenance changes in early Silurian times probably reflect the initiation of major tectonism in the Scandian Orogen to the northeast and, more locally, a change from a mineralized, extensional back-arc- to a foreland-basin environment as the Laurentian plate overrode Avalonia. Very similar geochemical trends extending from the highest Silurian strata in the Southern Uplands into the Windermere Supergroup of the English Lake District are consistent with sequential deposition in the same foreland basin. The principal crustal boundaries indicated by the geochemical data are the Moine Thrust Zone, the Grampian-Appin groups’ boundary, the Highland Boundary Fault and the Southern Upland Fault. The geochemical evidence provides little support for the Great Glen Fault as a significant terrane boundary, while the Iapetus Suture is shown to be a complex transition zone extending across the Southern Uplands and into the south of the Lake District. Within the former, the Moffat Valley Fault is identified as a major structure of regional significance. Throughout the orogen there is a direct relationship between geochemistry, tectonic setting and the presence of significant metalliferous mineralization.

Multielement regional geochemical reconnaissance as an aid to target selection in Irish Caledonian terrains

A regional geochemical reconnaissance, based upon the minus 150 micron fraction of active stream sediment, has been conducted by the Geological Survey of Ireland (GSI) over Irish Caledonian terrains. Thirty-eight chemical elements of economic and environmental significance (Ag, As, Au, Ba, Br, Cd, Ce, Co, Cr, Cs, Cu, Eu, Fe, Hf, Ir, La, Li, Lu, Mn, Mo, Na, Ni, Pb, Rb, Sb, Sc, Se, Sm, Sr, Ta, Te, Th, U, V, W, Yb, Zn and Zr) were determined by combined instrumental techniques (AAS and INAA). To date, the multielement database for some 2500 samples from three regions covers about 7,500 km 2. Data analysis employed resistant non-parametric techniques, or EDA (Exploratory Data Analysis) for objectively selecting outlier values (anomalies) and class boundaries for the distribution of each element. Such techniques are considered more appropriate to the treatment of geochemical data where assumptions about normality are rarely, if ever, achieved. Class selection was based on the resistant selected order statistic as represented in the boxplot. Special EDA mapping symbols, designed to give equal weighting to all data values, were assigned to the relatively wide boxplot class intervals. None of the original data are redundant in the resulting geochemical maps and, in many instances subtle regional variations can be recognized which are directly attributable to lithological variation. Outlier values are directly correlatable with known bedrock mineralization. The methodology was applied to data from two Caledonian terrains: the Inishowen area of northwestern Ireland and the Leinster massif of southeastern Ireland. A great diversity of metalliferous mineralization (Pb, Zn, Cu, Ba, Au, Ag, W, Li, Ta, U, Cr, Ni, Sb) is found in both terrains. The geochemical maps of Inishowen identify the most prospective gold-bearing lithologies quite effectively. In Leinster, the geochemical maps show the close spatial correlation of Li, Ta, U and W with granitic lithologies, the unequivocal volcanogenic signature of Cu, Sb and Au, an ultra-mafic Cr-Ni association and a new possible volcanogenic Zr-Hf association. While effective in identifying known bedrock mineralization, the maps also suggest possible extensions of mineralized zones and new targets for detailed follow-up surveys. The geochemical patterns defined on the maps are also of assistance in constraining metallogenic models. In addition it can be demonstrated that EDA-based techniques offer a viable and effective method of geochemical mapping.

Geochemical soil surveys as an aid to mapping and interpretation of the Lizard Complex

The results of a geochemical soil survey have been used to refine the geological mapping and interpretation of the inland, poorly exposed part of the Lizard Complex. Using cluster analysis, six major groups were recognized within a data set comprising 619 samples analysed for Cr, Co, Ni, Cu, Zn and Pb. These represented ultrabasic rocks, gabbroic rocks, two distinct units of Landewednack hornblende schist, metalliferous mineralization, and soils dominated by exotic material such as löess. The geographical distribution of these groups indicates that a lower Landewednack unit can be recognized in the S and W, separated by a thin transition zone from the main Lizard peridotite. This contrasts with its NE contact which is marked by a wide transition zone of soils suggesting interdigitating gabbroic and ultrabasic compositions, corresponding to the Traboe cumulate complex (Leake & Styles 1984), and a sharp contact with an Upper Landewednack unit. Both soil and deep auger sampling indicate that ultrabasic rocks underlie much of the area previously mapped as a tongue-like SW extension of the Crousa Gabbro.

Nature and distribution of metalliferous mineralization in the northern Antarctic Peninsula

Known mineralization in the N Antarctic Peninsula, although sparse, is comparable to that of the Andean metalliferous province. It includes porphyry-style Cu (MO and Fe) mineralization, polymetallic (Cu, Pb. Zn and Ag) veins, and a volcanogenic Fe deposit of Laco Sur type. Extensive areas of pyrite-rich hydrothermally altered rocks represent exposures of the high-level parts of porphyry copper systems. The known mineralization can be related to magmatism associated with subduction of the Pacific plate beneath the Antarctic Peninsula in the ?late Cretaceous and Cenozoic. A longitudinal distribution of metallogenic belts can be demonstrated; these are terminated by transverse tectonic boundaries which may reflect segmentation of the underlying subducted ocean plate. There is evidence that mineralization is concentrated along these tectonic boundaries.

Tectonic segmentation of the northern Antarctic Peninsula

Discrete segments of the southeast Pacific Ocean crust were subducted beneath the Antarctic Peninsula in Late Cretaceous and Cenozoic time. The segment boundaries of the subducted ocean crust are reflected in the overlying continental crust by transverse megafractures. These are usually obscured by contemporaneous magmatism but may be revealed by later fault movements. The transverse fracture zones divide Graham Land and its offlying islands into segments that have different histories of magmatism, uplift and erosion, and postorogenic sedimentation. Metalliferous mineralization is controlled, in part, by the transverse fracture zones.

Basement heat flow and metalliferous mineralization in England and Wales

Many examples of epigenetic metalliferous mineralization in central and northern England occur within a province now recognized to be characterized by high heat flow. Our analysis of this correlation leads us to conclude that Caledonian intrusive bodies, with high heat production and thermal conductivity, focused the development of hydrothermal systems responsible both for some types of post-Carboniferous mineralization and for present-day high heat flow.