Tin-bearing Granites Research Articles

The importance of sequential partial melting and fractional crystallization in the generation of syn-D3 Variscan two-mica granites from the Carrazeda de Ansiães area, northern Portugal

In the Carrazeda de Ansiães region, northern Portugal, a mesozonal granitic suite intruded Precambrian to Ordovician metasedimentary rocks during the late kinematic stages of the Variscan orogeny. In this multiphase granitic complex, consisting of ten granite types, the youngest group of two-mica granites (G7–G10) was emplaced between 318 ± 1 Ma and 316.2 ± 0.7 Ma, as determined by ID-TIMS U–Pb on zircon and monazite. Granite types G7–G9 were affected by the third phase of deformation (D3) before they were completely crystallized, as indicated by their internal NW–SE magmatic foliation concordant with the regional structures. The granite type G10 shows some distinctive textural features, showing a strong brittle deformation, probably due to its preferential emplacement in late NNE-SSW fault zones. Granites G7–G9 have equal or higher amounts of muscovite than biotite and contain surmicaceous enclaves, xenoliths, “schlieren”, and, more rarely, microgranular enclaves. The muscovite-dominant granite G10 does not contain enclaves. These Variscan granites are peraluminous, with ASI ranging between 1.22 and 1.39 and normative corundum of 2.79–4.39%, having the characteristics of S-type granites. In fact, the enrichment in LREE relatively to HREE, the negative Eu anomalies, and similar mean values of (87Sr/86Sr)i, εNdt and δ18O for G7 (0.7156 ± 0.0005; − 8.5; 11.49 ‰) and G8 (0.7155 ± 0.0007; − 8.4; 11.39 ‰) show that these two granite types resulted from sequential partial melting of the same metasedimentary material, where granite G8 would have derived from a higher degree of partial melting than G7. Granites G8–G10 and their minerals show a fractionation trend that is confirmed by modeling of major and trace elements. The subparallel REE patterns and the decreasing REE contents within the differentiation series, the Rb–Sr isochron for G8, G9 and G10 (315.5 ± 5.4 Ma; MSWD = 1.3) and the relatively uniform εNdt and δ18O data suggest that fractional crystallization was the main mechanism, which would have lasted less than 1 Ma. The tin-bearing granites G7 and G10 have ≥ 20 ppm Sn, but the main quartz veins containing cassiterite and wolframite cut granite G10, which contains 31 ppm Sn. Fractional crystallization was responsible for the increase in Sn content in granites from the G8–G10 series and their micas.

Granite-Related Tin Metallogenic Events and Key Controlling Factors in Peninsular Malaysia, Southeast Asia: New Insights from Cassiterite U-Pb Dating and Zircon Geochemistry

Abstract Permian-Triassic granites and associated tin deposits are widespread in the Eastern and Western belts of Peninsular Malaysia. The ages and key controlling factors of tin mineralization, however, are poorly constrained. Cassiterite separates from the Sintok and Rahman tin deposits in the Western belt, and Bandi, Setahum, Lembing, and Cherul tin deposits in the Eastern belt have U-Pb ages of 218.9 ± 3.4 and 226.8 ± 7.6 Ma, and 213.1 ± 3.9, 270.6 ± 4.6, 282.7 ± 4.6, and 281.3 ± 3.5 Ma, respectively. These ages directly constrain the tin mineralization in Peninsular Malaysia to two separate periods: 290 to 270 Ma and 230 to 210 Ma. Zircon crystals from tin-bearing granites in the Cherul and Sintok deposits have U-Pb ages of 276.0 ± 1.9 and 221.9 ± 0.6 Ma, respectively, consistent with the cassiterite U-Pb ages within uncertainties. Zircon crystals from barren granites of the Kuantan pluton in the Eastern belt have a U-Pb age of 260.5 ± 0.7 Ma, which is between the two tin mineralization periods. Zircon from these barren granites have εHf(t) values from −5.4 to 3.6, two-stage Hf model ages (TDM2) from 1.4 to 1.0 Ga, and Ce4+/Ce3+ ratios from 40 to 120. By comparison, zircon crystals from the tin-bearing granites have low εHf(t) values (−9.7 to −3.2) and Ce4+/Ce3+ ratios (4–67) and high TDM2 (1.8–1.4 Ga). Zircon ages, Hf isotopes, and trace elements indicate that the tin-bearing granitic magmas in Peninsular Malaysia had relatively low oxygen fugacity and were derived from reworking of Paleo- to Mesoproterozoic sedimentary rock-dominated crust in response to the Paleo-Tethyan subduction and continental collision. This study confirms that the nature of magma sources and redox states of magmas were key in the formation of the tin-rich granites and associated tin deposits and that the granite-related tin mineralization in Peninsular Malaysia was closely related to the evolution of the eastern Paleo-Tethys.

The Age, Sources, and Tectonic Setting of Tin-Bearing Granites of the Yazovka Complex of the Baikal–Patom Fold-Thrust Belt

The Age, Sources, and Tectonic Setting of Tin-Bearing Granites of the Yazovka Complex of the Baikal–Patom Fold-Thrust Belt

Geology and Geochronology of the Maozaishan Sn Deposit, Hunan Province: Constraints from Zircon U–Pb and Muscovite Ar–Ar Dating

The Maozaishan Sn deposit, located south of the Dayishan ore field in the Nanling Range, is a newly explored greisen-type Sn deposit. Two muscovite samples from tin-bearing ores yielded 40Ar/39Ar plateau ages of 154.7 ± 1.1 Ma (Mean standard weighted deviation (MSWD) = 0.48) and 152.6 ± 0.7 Ma (MSWD = 0.25), respectively. Zircon U–Pb dating result of fine-grained biotite monzogranite in the Maozaishan mining area shows that these zircon grains can be subdivided into two populations, with ages of 154.2 ± 2.0 Ma (MSWD = 0.51) and 159.6 ± 1.9 Ma (MSWD = 0.09), respectively, indicating that the monzogranite is formed by a multi-stage magmatic event. It is indicated that formation of the Maozaishan Sn deposit is closely related to the Middle Jurassic granitic magmatism. Based on the trace element compositions of zircon grains, the calculated magma temperatures and oxygen fugacity (log(fO2)) values range from 638 °C to 754 °C (mean = 704 °C) and from −18.9 to −15.8 (mean = −17.1), respectively. In addition, these intrusive rocks in the Dayishan ore field belong to highly fractionated granites and are characterized by low oxygen fugacity and crust–mantle origin, which are consistent to these tin-bearing granites in the Nanling Range and in favor of the Sn mineralization.

U-Pb monazite ages of the Kabanga mafic-ultramafic intrusions and contact aureoles, central Africa: Geochronological and tectonic implications

AbstractMafic-ultramafic rocks of the Kabanga-Musongati alignment in the East African nickel belt occur as Bushveld-type layered intrusions emplaced in metasedimentary sequences. The age of the mafic-ultramafic intrusions remains poorly constrained, though they are regarded to be part of ca. 1375 Ma bimodal magmatism dominated by voluminous S-type granites. In this study, we investigated igneous monazite and zircon from a differentiated layered intrusion and metamorphic monazite from the contact aureole. The monazite shows contrasting crystal morphology, chemical composition, and U-Pb ages. Monazite that formed by contact metamorphism in response to emplacement of mafic-ultramafic melts is characterized by extremely high Th and U and yielded a weighted mean 207Pb/206Pb age of 1402 ± 9 Ma, which is in agreement with dates from the igneous monazite and zircon. The ages indicate that the intrusion of ultramafic melts was substantially earlier (by ∼25 m.y., 95% confidence) than the prevailing S-type granites, calling for a reappraisal of the previously suggested model of coeval, bimodal magmatism. Monazite in the metapelitic rocks also records two younger growth events at ca. 1375 Ma and ca. 990 Ma, coeval with metamorphism during emplacement of S-type granites and tin-bearing granites, respectively. In conjunction with available geologic evidence, we propose that the Kabanga-Musongati mafic-ultramafic intrusions likely heralded a structurally controlled thermal anomaly related to Nuna breakup, which culminated during the ca. 1375 Ma Kibaran event, manifested as extensive intracrustal melting in the adjoining Karagwe-Ankole belt, producing voluminous S-type granites. The Grenvillian-aged (ca. 990 Ma) tin-bearing granite and related Sn mineralization appear to be the far-field record of tectonothermal events associated with collision along the Irumide belt during Rodinia assembly. Since monazite is a ubiquitous trace phase in pelitic sedimentary rocks, in contact aureoles of mafic-ultramafic intrusions, and in regional metamorphic belts, our study highlights the potential of using metamorphic monazite to determine ages of mafic-ultramafic intrusions, and to reconstruct postemplacement metamorphic history of the host terranes.

Formation and geodynamic implication of the Early Yanshanian granites associated with W–Sn mineralization in the Nanling range, South China: an overview

ABSTRACTThe Nanling range (Nanling) is characterized by intense and widespread Mesozoic magmatism related large-scale W–Sn mineralization. A summary of geochemistry, geochronology, and petrogenesis for the W–Sn-bearing granites has been carried out in this study. A series of rock- and ore-forming ages in Nanling indicate that the W–Sn mineralization is closely related to the Early Yanshanian granitic magmatism both in temporal and spatial dimensions (165–150 Ma). Geochemical features show that both of the W- and Sn-bearing granites, which mainly belong to highly fractionated I-type granites with a few A-type granites, are characterized by high contents of SiO2, Al2O3, Na2O, and K2O; enrichment in Rb, Th, U, Zr, Hf, and REE; depletion in Sr, Ba, P, and Ti; and high ratios of A/CNK. Furthermore, the different Sr–Nd–Hf isotopic compositions indicate that they are mainly originated from the partial melting of the Precambrian basement rocks of the Cathaysia Block at low oxygen fugacity, and the estimated temperatures for the tungsten-bearing and tin-bearing granites are ca. 700°C and ca. 800°C, respectively. The model of the mantle–crust interaction exhibits that different percentages of mantle-derived magma were likely involved in the generation of the tin-bearing granites and tungsten-bearing granites. In combination with previous studies, we propose that these granites in Nanling were emplaced in an extensional setting, as a response to the break-off and roll-back of the subducted Palaeo-Pacific Plate during 175–150 Ma.

Diversity of Mesozoic tin-bearing granites in the Nanling and adjacent regions, South China: Distinctive mineralogical patterns

The Nanling and adjacent regions of South China host a series of tin deposits related to Mesozoic granites with diverse petrological characteristics. The rocks are amphibole-bearing biotite granites, or (topaz-) albite-lepidolite (zinnwaldite) granites, and geochemically correspond to mealuminous and peraluminous types, respectively. Mineralogical studies demonstrate highly distinctive and critical patterns for each type of granites. In mealuminous tin granites amphibole, biotite and perthite are the typical rock-forming mineral association; titanite and magnetite are typical accessory minerals, indicating high f O2 magmatic conditions; cassiterite, biotite and titanite are the principal Sn-bearing minerals; and pure cassiterite has low trace-element contents. However, in peraluminous tin granites zinnwaldite-lepidolite, K-feldspar and albite are typical rock-forming minerals; topaz is a common accessory phase, indicative of high peraluminity of this type of granites; cassiterite is present as a uniquely important tin mineral, typically rich in Nb and Ta. Mineralogical distinction between the two types of tin granites is largely controlled by redox state, volatile content and differentiation of magmatic melts. In oxidized metaluminous granitic melts, Sn4+ is readily concentrated in Ti-bearing rock-forming and accessory minerals. Such Sn-bearing minerals are typical of oxidized tin granites, and are enriched in granites at the late fractionation stage. In relatively reduced peraluminous granitic melts, Sn2+ is not readily incorporated into rock-forming and accessory minerals, except for cassiterite at fractionation stage of granite magma, which serves as an indicator of tin mineralization associated with this type of granites. The nature of magma and the geochemical behavior of tin in the two types of granites thus result in the formation of different types of tin deposits. Metaluminous granites host disseminated tin mineralization, and are locally related to deposits of the chlorite quartz-vein, greisen, and skarn types. Greisen, skarn, and quartz-vein tin deposits can occur related to peraluminous granites, but disseminated mineralization of cassiterite is more typical.

Evidence for aqueous liquid-liquid immiscibility in highly evolved tin-bearing granites, Mount Pleasant, New Brunswick, Canada

Three distinct types of fluid inclusions (i.e., liquid+vapor (LV), liquid+vapor+solid (LVS), and V-only) co-exist within a single, primary fluid inclusion assemblage in fluorite crystals that formed prior to and in close association with cassiterite mineralization in an assemblage comprising fluorite+arsenopyrite+topaz+cassiterite in the Sn (-W-Mo) deposit of the North Zone, Mount Pleasant, New Brunswick. The mineral assemblage occurs in vugs, with late quartz and chlorite filling the remainder of the open space. Solid-bearing inclusions contain up to eight, optically different solids, which are estimated to occupy up to approximately 70vol.% of the fluid inclusions. In a given fluid inclusion assemblage, each type of fluid inclusion shows consistent L-V or L-V-S phase ratios.The results of microthermometric analyses show that LV inclusions have low salinities that vary from 0 to 10wt.% NaCl eq., and homogenization temperatures that vary from 91 to 250°C. Within a given assemblage, the ranges of salinity and homogenization temperatures of LV inclusions are even less. In contrast, co-existing LVS inclusions are highly saline, with salinities ranging from 36 to 40wt.% NaCl eq., and have much higher homogenization temperatures that vary from 425°C to >600°C (the upper limit of the microthermometric stage). The salinity and homogenization temperature ranges of LVS inclusions show a limited range for a given assemblage. The solids in LVS inclusions are interpreted as daughter phases due to consistent phase ratios in LVS fluid inclusions and because, during heating experiments, all solid phases melted prior to liquid-vapor homogenization. The consistency of phase ratios and the results of microthermometric analysis among LV or among LVS inclusions show that these inclusions were not formed through necking down of larger inclusions. In addition, the absence of ‘sweat halos’ and re-entrants rules out water loss as a possible mechanism for producing these coexisting fluid inclusions. Fluid inclusions of highly contrasting salinities and homogenization temperatures are, therefore, interpreted to be the result of trapping from two, immiscible, aqueous liquids. It is unknown whether the two liquids exsolved from one single, aqueous fluid or have different origins, but consideration of the nature of inclusion assemblages in samples from other parts of the system, suggest the latter. Topaz and cassiterite within the same mineral assemblage, as well as late quartz, contain LV fluid inclusion assemblages with microthermometric behaviors that are similar to the LV type inclusions in coexisting, fluorite-hosted, LV and LVS inclusions, suggesting that cassiterite deposited from the low salinity and temperature fluid.

Petrogenesis of Malaysian granitoids in the Southeast Asian tin belt: Part 2. U-Pb zircon geochronology and tectonic model

In our complementary geochemical study (Part 1), the Malaysian granitoids of the Southeast Asian tin belt were divided into a Middle Permian to Late Triassic I-type–dominated Eastern province (Indochina terrane) and a Triassic to Early Jurassic transitional I/S-type Main Range province (Sibumasu terrane), separated by the Bentong-Raub suture zone which closed in the Late Triassic. Previous geochronology has relied on only a few U-Pb zircon ages together with K-Ar and whole rock Rb-Sr ages that may not accurately record true magmatic ages. We present 39 new high-precision U-Pb zircon ion microprobe ages from granitoids and volcanics across the Malay Peninsula. Our results show that ages from the Eastern province granitoids span 289–220 Ma, with those from the Main Range province granitoids being entirely Late Triassic, spanning 227–201 Ma. A general westerly younging magmatic trend across the Malay Peninsula is considered to reflect steepening and roll-back of the Bentong-Raub subduction zone during progressive closure of Paleo-Tethys. The youngest ages of subduction-related granites in the Eastern province roughly coincide with the youngest ages of marine sedimentary rocks along the Paleo-Tethyan suture zone. Our petrogenetic and U-Pb zircon age data support models that relate the Eastern province granites to pre-collisional Andean-type magmatism and the western Main Range province granites to syn- and post-collisional crustal melting of Sibumasu crust during the Late Triassic. Tin mineralization was mainly associated with the latter phase of magmatism. Two alternative tectonic models are discussed to explain the Triassic evolution of the Malay Peninsula. The first involves a second Late Triassic to Jurassic or Early Cretaceous east-dipping subduction zone west of Sibumasu where subduction-related hornblende and biotite–bearing granites along Sibumasu are paired with Main Range crustal-melt tin-bearing granites, analogous to the Bolivia Cordilleran tin-bearing granite belt. The second model involves westward underthrusting of Indochina beneath the West Malaya Main Range province, resulting in crustal thickening and formation of tin-bearing granites of the Main Ranges. Cretaceous granitoids are also present locally in Singapore (Ubin diorite), on Tioman Island, in the Noring pluton, of the Stong complex (Eastern Province), and along the Sibumasu terrane in southwest Thailand and Burma (Myanmar), reflecting localized crustal melting.

Late Cretaceous granites from the giant Dulong Sn-polymetallic ore district in Yunnan Province, South China: Geochronology, geochemistry, mineral chemistry and Nd–Hf isotopic compositions

As a world-class tin–tungsten province, South China is well known for its extensive Mesozoic granitic magmatism. The Dulong district, located in the western Cathaysia Block of the South China tin–tungsten province, is characterized by widespread Mesozoic granitoids and accompanying Sn-polymetallic ore deposit (~30 Mt of Sn). It is one of the most important polymetallic tin ore districts in China. In this study, three mineralization-related granite types were identified in the Dulong district, including the Dulong coarse-grained granite (DCG), the Dulong fine-grained granite (DFG), and the Dulong porphyritic granite (DPG). Detailed studies are presented on zircon U–Pb ages, major and trace elements, mineral chemical and Nd–Hf isotopic compositions of the tin-bearing granites from the Dulong district. LA-ICP-MS U–Pb dating of zircon grains from these three granite bodies yields ages of 90.1±0.7Ma, 89.7±0.8Ma and 86.0±0.5Ma, respectively. Geochemically, the granites are strongly peraluminous, with high contents of alkalis, enrichment in P, Li, Rb, Cs, Ta, Sn, W and U, depletion in Ti, Mg, Co, Ni, Sr, Ba, Zr, Hf, Th and rare earth elements. Fractional crystallization of plagioclase and K-feldspar was the principal process of magmatic differentiation that controlled Rb, Sr, Ba and Eu concentrations, whereas rare earth elements were fractionated by accessory minerals, such as apatite and monazite. The geochemical data suggest that the rocks are highly fractionated S-type granites. The granites show bulk rock εNd(t) values in the range of −12.2 to −10.8 and zircon εHf(t) values from −15.5 to −2.5, with Meso-Paleoproterozoic TDMC ages for both Nd and Hf isotopes. Geochemical and isotopic data suggest that these highly fractionated S-type granites DCG, DFG and DPG were originated from the same episode of partial melting of the protolith, which have analogous components of metamorphosed pelitic rocks from the Meso-Paleoproterozoic continental crust. Extreme fractional crystallization resulted in enrichment of tin in the evolved granitic magma, and the reduced magmas (fO2 below NNO) would efficiently remove Sn into a hydrothermal fluid, and lead to deposition of Sn-rich mineral phases. The association of Dulong and Gejiu magmatism in the western Cathaysia Block may be likely to mark the onset of back-arc extension or intra-arc rift in the region during Late Cretaceous. The upwelling of asthenospheric mantle may have triggered partial melting of metasedimentary rocks in the overlying crust to generate the S-type granitic magmas.

Late Variscan calc-alkaline lamprophyres in the Krupka ore district, Eastern Krušné hory/Erzgebirge: their relationship to Sn-W mineralization

*Corr esponding author Variscan lamprophyres occur in the greisen tin-, tungsten- and molybdenum-ore district of Krupka in the Eastern Krusne hory/Erzgebirge (KHE). They belong to a bimodal dyke suite of aplites, felsic porphyries, microgranites and mafic dykes associated with late Variscan tin-bearing granites and include minettes, kersantites and spessartites, while vogesite reported earlier has not been confirmed. One altered mafic dyke is interpreted as original microdiorite. All lamprophyres are basic to intermediate rocks (47.3–56.9 wt. % SiO 2 ) with shoshonitic to ultrapotassic composition (3.1–7.5 wt. % K 2 O). The high concentrations of MgO (4.7–11.4 wt. %), molar Mg/(Mg + Fe) ratios (0.56–0.74) and abundances of compatible elements (350–800 ppm Cr, 130–360 ppm Ni) indicate that lamprophyres represent primary mantle melts that underwent no or little fractionation or contamination, and high LREE/HREE ratios point to magma formation in the stability field of garnet peridotite. In addition, high contents of potassium and LILE (50–370 ppm Li, 150–920 ppm Rb, 750–3100 ppm Ba) indicate metasomatic enrichment of the upper mantle prior to partial melting. The LILE–HFSE–REE patterns indicate involvement of slab components (subducted siliciclastic and carbonate sediments). Strong enrichment in U (6–29 ppm) and Th (17–75 ppm) is another characteristic feature of lamprophyres from the Eastern KHE and elsewhere in central Europe, and it is consistent with the metasomatic transport via oxidized saline fluids from the slab to the mantle wedge. The lamprophyres in the Krupka district were variably greisenized in the vicinity of granite greisens and Sn–W hydrothermal veins and their original minerals were replaced by an assemblage of lithian phlogopite, topaz, fluorite, apatite and titanium-bearing phases. During alteration, they were strongly depleted in Na 2 O, CaO, Sr and Ba, moderately depleted in REE, and enriched in Li, Rb, Cs, Sn and F. By contrast, Al and Zr behaved as immobile elements and their abundances indicate overall mass loss of 10–18 % during greisenization consistent with the increase of porosity, which facilitated the hydrothermal dissolution–precipitation reactions. The spatial association of greisens and lamprophyres suggests that the greisenizing fluids migrated along similar geological structures, which were previously accessible to the mantle-derived media (melts and/or fluids). On a local scale, the lamprophyre dykes intersected by greisen veins provided geochemical or lithological barrier, which favoured the cassiterite deposition. The timing of lamprophyre dykes also indicates that the mantle metasomatism beneath the KHE area occurred before the late Variscan granitic magmas were generated.

U–Pb zircon geochronology of Early Permian to Late Triassic rocks from Singapore and Johor: A plate tectonic reinterpretation

The results of U–Pb zircon geochronology of Permian to Middle Triassic granitoids from Singapore and neighbouring Johor are presented. Rhyolite from Pulau Sibu is 276±5Ma, gabbros from Singapore give ages of 260±2 to 249±2Ma, granites from Singapore give ages from 249±2 to 230±6Ma and rhyolite from Telkuma gives an age of 238±2Ma.U–Pb detrital zircon age spectra from a Late Triassic conglomerate from Singapore show Carboniferous, Middle Triassic and Late Triassic spikes at 350, 245 and 217Ma respectively. These new data, when combined with published U–Pb zircon ages, allow a revision of the plate tectonic evolution of the Malaysian Peninsula region. A tin-bearing magmatic arc evolved in the Eastern Malaysian Peninsula part of Indochina from the Early Permian to the Middle Triassic when the Palaeo Tethys Ocean was subducted and Sibumasu continental lithosphere was rifted from Pangea. This opened up the Neo Tethys Ocean. That the granitoid ages show a progressive decrease in age from Pulau Sibu (276±5Ma) to Singapore (230±6Ma) suggests that during this Andean-type orogenic phase, the subduction zone rolled back and steepened causing the locus of mainly I-type magmatism to migrate from east to west (in present day coordinates) across the Eastern and Central Belts and stretch the lithosphere as it did so. In the Late Triassic, Sibumasu collided with Indochina causing the Western Belt (Sibumasu) to over-thrust the Central Belt (Indochina) along the Bentong–Raub Suture. The lower half of the thickened crust (formally the tin-bearing Indochina Plate) was partially melted and predominantly S-type tin-bearing granites were intruded into the upper crust (formally Sibumasu). This Late Triassic collisional phase is the Indosinian Orogeny in Peninsular Malaysia.

The timing of strike-slip shear along the Ranong and Khlong Marui faults, Thailand

[1] The timing of shear along many important strike-slip faults in Southeast Asia, such as the Ailao Shan-Red River, Mae Ping and Three Pagodas faults, is poorly understood. We present 40Ar/39Ar, U-Pb SHRIMP and microstructural data from the Ranong and Khlong Marui faults of Thailand to show that they experienced a major period of ductile dextral shear during the middle Eocene (48–40 Ma, centered on 44 Ma) which followed two phases of dextral shear along the Ranong Fault, before the Late Cretaceous (>81 Ma) and between the late Paleocene and early Eocene (59–49 Ma). Many of the sheared rocks were part of a pre-kinematic crystalline basement complex, which partially melted and was intruded by Late Cretaceous (81–71 Ma) and early Eocene (48 Ma) tin-bearing granites. Middle Eocene dextral shear at temperatures of ∼300–500°C formed extensive mylonite belts through these rocks and was synchronous with granitoid vein emplacement. Dextral shear along the Ranong and Khlong Marui faults occurred at the same time as sinistral shear along the Mae Ping and Three Pagodas faults of northern Thailand, a result of India-Burma coupling in advance of India-Asia collision. In the late Eocene (<37 Ma) the Ranong and Khlong Marui faults were reactivated as curved sinistral branches of the Mae Ping and Three Pagodas faults, which were accommodating lateral extrusion during India-Asia collision and Himalayan orogenesis.

Mineralogical evidence for magmatic and hydrothermal processes in the Qitianling oxidized tin-bearing granite (Hunan, South China): EMP and (MC)-LA-ICPMS investigations of three types of titanite

The Qitianling granite, which is located in Hunan Province (southern China), is a metaluminous Sn granite that crystallized at relatively oxidized conditions, between the Ni–NiO (NNO) and Fe 2O 3–Fe 3O 4 (MH) buffers. Titanite (sphene, CaTiSiO 5) is a common tin-carrier mineral in the Qitianling granite. Based on electron-microprobe (EMP) and multi-collector (MC)-Laser-ablation (LA)-ICPMS investigations, we describe three types of titanite with various textures and SnO 2 contents, which probably formed during the magmatic and hydrothermal processes responsible for the granite crystallization and later evolution. The form of type I titanite ranges from subhedral to euhedral coarse-grained crystals and typically exhibits an envelope-like shape and sector-zoning. It is characterized by a high Fe 2O 3 content (on average 2.44 wt.%) and low SnO 2 (0.43 wt.%), which indicates crystallization during an early magmatic stage. Its formation temperature is estimated to have been 721 to 780 °C from EMP- and LA-ICPMS using the Zr-in-titanite geothermometer. Type II titanite occurs as both discrete grains and symplectitic intergrowths; and typically fills interstices between other minerals. It contains up to 26 wt.% SnO 2, which suggests a late magmatic origin. Chondrite-normalized REE patterns for type II titanite reveal a lanthanide tetrad effect that was linked to differentiation of the granite magma. Type III titanite is restricted to cleavage cracks in chlorite and is rich in Al 2O 3. It is obviously the secondary product of biotite alteration at a temperature that is estimated to be lower than 400 °C during the hydrothermal stage. This hydrothermal activity also impacted the primary titanites. Type I titanite experienced alteration to different degrees via coupled dissolution–reprecipitation, which gave rise to the formation of secondary minerals including cassiterite micro-grains. Some grains of the type II titanite reacted with fluids along the grain boundary, which led to the gradual leaching of Sn. Based on information from these types of titanite and their Sn behavior, we discuss the progressive enrichment of Sn during and after granite crystallization under a high oxidation state as well as the predominant role of fluids in the leaching, concentration and transportation of Sn during hydrothermal processes, which favors vein-type Sn mineralization.

Geochemistry of waters associated with the old mine workings at Fonte Santa (NE of Portugal)

The quartz veins containing scheelite from Fonte Santa mine cut the Lower Ordovician quartzites. A muscovite–biotite granite (G1) and a muscovite granite (G2), both S-type, crop out close to the Fonte Santa mine and are related to the Moncorvo–Bemposta shear zone. The most altered samples of G2 show intense muscovitization and microclinization and contain chlorite, columbite–tantalite, wolframite, W-ixiolite and Fe-oxides. The tin-bearing granites contain 18 ppm (G1) and 73 ppm (G2) Sn. The most altered samples of G2 correspond to a tungsten granite. The quartz veins contain muscovite, chlorite, tourmaline, scheelite, pyrrhotite, pyrite, sphalerite, chalcopyrite, galena, arsenopyrite, iron oxides, Fe sulfates, phosphates of Pb, Fe and Al. The Fonte Santa mine area was exploited for W between 1942 and 1982. At the end of November 2006, a flood event damaged the tailings dam of Fonte Santa mine, releasing contaminated material and increasing contaminant levels in water within the area of influence of the mine. The waters related to the Fonte Santa mine are poorly mineralized, with electrical conductivity of < 965 µS/cm, and of a mixed type or HCO 3 − and SO 4 2− types. Most pH values (5.0−8.5) indicate that there is no significant acidic drainage in the region, as found in other areas. More acidic values (pH = 3.4) were found in the mine's lagoon. Waters associated with mineralized veins and old mine activities have Fe and Mn concentrations that forbid their use for human consumption and agriculture. Natural Na, Mg and K water contents are associated with the alteration of albite, chlorite and muscovite of country rock, while Ca with the W-bearing quartz veins. Weathering agents are carbonic and sulphuric acids and the latter has a strong influence in areas draining fine-grained mine tailings.

A Review on Permian to Triassic Active or Convergent Margin in Southeasternmost Gondwanaland: Possibility of Exploration Target for Tin and Hydrocarbon Deposits in the Eastern Indonesia

http://dx.doi.org/10.17014/ijog.vol4no1.20094An active convergence of continental margin is probably generated in Gondwanaland during Permian to Triassic period which is characterized by the presence of magmatic and volcanic belts and back-arc ba- sins occupied respectively by Permian to Triassic rocks. The magmatic belt is occupied by peraluminous granitic plutons showing characteristics of S- type granite and is considered as tin-bearing granites. The back-arc basins are occupied by the Southern Papua and Galille-Bowen-Gunnedah-Sydney Basins. Those large basins are respectivelly filled by fluvial, fluvio- deltaic to marine Permian-Triassic sediments, which are unconformably overlain by the Jurrassic-Cretaceous marine succession. The paleomagnetic data, confirmed by flora content found in Australia and Papua, indicate that those areas initially belong to the Gondwanaland before part of them were drifted and rotated into the present day position. Tectonically, the presence of those Permian-Triassic magmatic-volcanic belts and back-arc basins in behind, indicates that at the time there were huge compressive activities: convergence of paleo-oceanic Pasific Plate moving westward, collided and subducted into the Southeastern Gondwana Continental Plate, moved relatively eastwards. This phenomenon resembles to the formation of Sumatera Tertiary tectonic zones producing back-arc basins, i.e. South Sumatera, Central, and North Sumatera Basins including the Tertiary Magmatic Arc. Concerning the similarity of Permian-Triassic geological condition of the magmatic arc and back-arc basins in Eastern Indonesia and Eastern Australia including paleoposition, paleotectonic setting, strati- graphic succession, and lithologic composition, it is suggested to carry out an increase in a more intens- ive tin exploration in the Eastern Indonesia, e.g. Bird Head area and Banggai Sula Island, and also for hydrocarbon target (coal, coalbed methane, oil and gas, and oil shale) in the Southern Papua Basin, East Indonesia. This suggestion is confirmed by cassiterite and hydrocarbon discoveries and exploitation activ- ity in the Eastern Australia and also a new seismic data of the Semai Basin a part of Southern Papua Basin. This seismic record shows a more complete stratigraphic sucession and a number of large structure traps of stratigraphic levels in which the Permian-Triassic units are included within the sequence.

Variações composicionais de zircão em granitos anorogênicos proterozóicos do Cráton Amazônico: implicações metalogenéticas

Hf-rich zircons in granitic rocks are typically associated with evolved, rare metals (Sn, Nb, Ta, W) specialized-granites. Zircons of topaz and rare-metal-bearing granites displays extremely low Zr/Hf ratios that are interpreted as a magmatic signature inherited of evolved granitic melts or as the result of hydrothermal alteration of the host rocks by F-rich fluids. This study is based essentially on images of zircon crystals, obtained through a SEM, and on semi-quantitative Energy Dispersive Spectrometry (EDS) analyses. The analyzed zircon crystals are of tin-specialized granitoids of distinct tin provinces of the Amazonian craton: the South Para, Pitinga, and Rondonia tin provinces. Zircon compositions of the A-type, not tin-mineralized granites of the Jamon Suite, southeastern of the Amazonian craton, and the Santa Rosa Granite, of the Xingu region are also presented for comparison. The zircon of the tin-specialized granites is characteristically enriched in Hf, Y, U, and Th and displays lower Zr/Hf ratios toward the more evolved facies, suggesting that magmatic differentiation was responsible for this particular feature. The zircons of the not mineralized granites show lower contents of these elements and comparatively high Zr/Hf ratios. The characteristic geochemical signature in zircons of the Tin-specialized granites indicate that zircon composition can be a useful guide to evaluate the metallogenetic potential of tin-bearing granites. A preliminary evaluation of the potential for tin in evolved granites may be based on zircon compositional studies employing EDS semi-quantitative analices obtained with a SEM. This can be an important tool for exploration surveys.

Variações composicionais de zircão em granitos anorogênicos proterozóicos do Cráton Amazônico: implicações metalogenéticas

Hf-rich zircons in granitic rocks are typically associated with evolved, rare metals (Sn, Nb, Ta, W) specialized-granites. Zircons of topaz and rare-metal-bearing granites displays extremely low Zr/Hf ratios that are interpreted as a magmatic signature inherited of evolved granitic melts or as the result of hydrothermal alteration of the host rocks by F-rich fluids. This study is based essentially on images of zircon crystals, obtained through a SEM, and on semi-quantitative Energy Dispersive Spectrometry (EDS) analyses. The analyzed zircon crystals are of tin-specialized granitoids of distinct tin provinces of the Amazonian craton: the South Pará, Pitinga, and Rondônia tin provinces. Zircon compositions of the A-type, not tin-mineralized granites of the Jamon Suite, southeastern of the Amazonian craton, and the Santa Rosa Granite, of the Xingu region are also presented for comparison. The zircon of the tin-specialized granites is characteristically enriched in Hf, Y, U, and Th and displays lower Zr/Hf ratios toward the more evolved facies, suggesting that magmatic differentiation was responsible for this particular feature. The zircons of the not mineralized granites show lower contents of these elements and comparatively high Zr/Hf ratios. The characteristic geochemical signature in zircons of the Tin-specialized granites indicate that zircon composition can be a useful guide to evaluate the metallogenetic potential of tin-bearing granites. A preliminary evaluation of the potential for tin in evolved granites may be based on zircon compositional studies employing EDS semi-quantitative analyses obtained with a SEM. This can be an important tool for exploration surveys.

Bainiuchang super-large silver-polymetallic ore deposit related to granitic magmatism in Mengzi, Yunnan

Bainiuchang silver-polymetallic ore deposit is located in the southeast Yunnan tin-polymetallic metallogenic belt. The probable reserves and inferred resources of the deposit are of 6 470 t Ag and 1.10 Mt Pb and 1.72 Mt Zn and 86 kt Sn. Orebodies of the deposit occur in clastic-carbonate rocks of Tianpeng Formation and Longha Formation of the middle Cambrian System above the Bainiuchang concealed granite of the late Yanshan period. The concealed granite has the characteristics of tin-bearing granites. Abundance of the mineralization elements Sn, Cu, Zn, Pb, Ag and Sb is high in the granitic rocks. Sulphur isotope data of the metal sulphides indicate that most sulphur is derived from the magmas. The ores are similar in rare earth element(REE) patterns to the granitic rocks. The granitic magma activity results in ore-bearing structures. Rocks of the Middle Cambrian System above the concealed intrusion suffer from skarnization, hornfelsing, marbleization, siliconizing and carbonatization. The mineralization elements Sn, Cu, Zn, Pb, Ag and Sb successively appear from the top of the granite to surrounding rocks. These evidences indicate that the granitic magmatism is the principal mineralization factor. The opinion that the south Bainiuchang ore field and the north Awei ore block are tin and copper potential exploration areas was put forward and was verified by drilling tests.

The origin and mineralization of the tin-bearing granites of the Krusné hory (Erzgebirge) province: A 3-dimensional approach with new data on ore deposit zoning around a granite batholith

The new summary of metallogeny of the Erzgebirge/Krusne hory granite batholith (Sn, W, U, Pb-Zn, Ag, Bi, Co, Ni, fluorite and barite) in Central Europe shows that the symmetrical and synchronous mineral zones around the granitic magmatic foci of temperature and pressure do not exist. The irregular distribution of mineral districts is controlled by the lines of emplacement of younger (YIC) granites, by major deep-seated fault zones and by the local lithology in the envelope. Variously mineralized crustal segments were exposed to different fluids of various origin after the emplacement of granites. This is the main cause for the irregular distribution of ore-bearing assemblages in relation to the granites which early workers interpreted as horizontal mineral zoning.