Résumé : Des analyses complètes des éléments traces de roches volcaniques mafiques et felsiques p... more Résumé : Des analyses complètes des éléments traces de roches volcaniques mafiques et felsiques provenant de la ceinture de roches vertes Meen-Dempster, 2,85–2,74 Ga, montrent une grande diversité de composition. L'assemblage Kaminiskag,2,85 Ga, est dominé par une tholéiite ...
... Mike Easton, Pete Hollings, and Wally Rayner ... Hart and MacDonald (2007) summarize the resu... more ... Mike Easton, Pete Hollings, and Wally Rayner ... Hart and MacDonald (2007) summarize the results arising from 1:50000-scale bedrock mapping conducted west of Lake Nipigon in 2003 and 2004 (Hart and Magyarosi 2004; MacDonald 2004; Hart 2005a; MacDonald et al. 2005). ...
During a five week period, 19 caves were explored by a team of four cavers comprising the 1994 Me... more During a five week period, 19 caves were explored by a team of four cavers comprising the 1994 Mendip Caving Group (MCG) expedition to Belize. Six sizable caves were identified in the Cretaceous limestone, west of the Maya Mountains, and surveyed a total length of 2.5 km. Time spent in the field is broken down so as to show both the advantages and disadvantages of a small-scale expedition. Suggestions are made as to how future groups could benefit from the experiences of the expedition with regard to conducting significant research with a small team. The MCG expedition is compared to other larger expeditions, with the results showing that lightweight expeditions are more easily financed and organized than larger expeditions; however, they may not be suitable if detailed scientific studies are intended.
The Caixiashan giant carbonate-hosted Zn-Pb deposit (~131 Mt@ 3.95% Zn + Pb) formed by replacemen... more The Caixiashan giant carbonate-hosted Zn-Pb deposit (~131 Mt@ 3.95% Zn + Pb) formed by replacement of dolomitized marble, with stratiform massive and breccia bodies is located near the base of the Proterozoic Kawabulake Group limestone and marble. It is one of the largest carbonated-hosted massive sulfides Zn-Pb ore deposits in Northwest China to have been discovered in recent years. Abundant pyrite occurs in dolomitized marble, along fractures in dolomitized clasts in the host rocks and filling cracks in the host rock. Locally, colloform or framboidal pyrites are observed in the early period and sometimes replaced by the later sphalerite. The sulfide assemblage of the main ore stage is characterized by massive or disseminated sphalerite and galena, with less pyrite than the earlier stage, and minor pyrrhotite. Galena occurs as small veins cutting the early-formed sphalerite. Dolomite and calcite are the main gangue minerals that coprecipitated with these sulfides. Tremolite and quartz alteration commonly overprints the orebodies. According to the crosscutting relationships and the different mineral associations within the host rocks and ore bodies, three stages are recognized at Caixiashan, i.e., syn-sedimentary pyrite (stage I), pyrite alteration, sphalerite-carbonate and galena-pyrite-carbonate (stage II-1, stage II-2 and stage II-3, respectively) and magmatic/metamorphic reworking (stage III). Calcite and quartz crystals are important host minerals among the three hypogene stages (stages I-III, although quartz mainly occurred in stage III). Stage I contains only aqueous inclusions (W-type), which were homogenized from 110 to 236°C (main range of 138-198°C and average at 168°C; main range = average ± σ) and the salinities are from 0.5 to 16.5 (main range of 5.1-15.1 with average of 10.1) wt.% NaCl eqv. In the pyrite alteration of stage II-1 the W-type fluid inclusions homogenized from 175 to 260°C (main range of 210-260 with average of 235) and the salinities range from 8.5 to 22.4 (main range of 16.7-20.1 with average of 18.4) wt.% NaCl eqv. In the main Zn-Pb mineralization stage (stage II-2-3), four types of fluid inclusions were identified an aqueous phase (W-type), a pure carbon phase (PC-type), a carbon phase containing (C-type) and mineral bearing inclusions (S-type). The W-type fluid inclusions of stage II-2-3 homogenized at 210 to 370°C (main range of 253-323 and average at 270) and the salinities range from 5.9 to 23.1 (main range of 13.3-20.3 with average at 16.8) wt.% NaCl eqv.; C-type homogenized at 237°C to 371°C and the salinities range from 6.4-19.7 wt.% NaCl eqv.; S-type fluid inclusions homogenized at 211 to 350°C and daughter minerals melted between 340 and 374°C during heating, indicating a salinity range of 42 to 44 wt.% NaCl eqv. PC-type fluid inclusions with homogenization temperatures of CO 2 phase show large variation from 7.4°C to 21.2°C. Laser Raman analyses show that CH 4 , CO 2 and SO 4 2 − coexist in the main mineralization stage fluids. The magmatic/metamorphic reworking stage only contains W-type fluid inclusions which yield homogenized between 220 and 360°C (main range of 251-325 and average at 288), with salinities ranging from 1.7 to 23.0 (main range of 14.3-20.0 and average at 18.8) wt.% NaCl eqv. The textural features, mineral assemblages and fluid geochemistry suggest that the Zn-Pb ores were formed through hydrothermal convection of hot marine waters along the faults and fractures resulting in metal (Zn, Ore Geology Reviews 72 (2015) [355][356][357][358][359][360][361][362][363][364][365][366][367][368][369][370][371][372] Pb and Fe) enriched stratiform orebodies. Subsequent rapid precipitation of sulfides was triggered by sulfate (SO 4 2− ) thermal reduction with the CH 4 preserved in sedimentary rocks and early stage I pyrite bodies. This process occurred at moderate temperatures (ca. 270°C). Higher-temperature magmatic hydrothermal alteration overprinted the orebodies, but only provided a minor contribution to the mineralization.
The Huangshan mafic-ultramafic intrusion hosts a large Ni-Cu sulfide deposit and is situated in t... more The Huangshan mafic-ultramafic intrusion hosts a large Ni-Cu sulfide deposit and is situated in the Northern Tianshan at the southern margin of the Central Asian Orogenic Belt (CAOB). The Early Permian intrusion consists of lherzolite, websterite, gabbronorite, gabbro and diorite. The Huangshan deposit contains~80.4 Mt of ore grading 0.54 wt.% Ni and 0.3 wt.% Cu and is the second largest magmatic sulfide deposit in Northern Xinjiang, China. The Huangshan intrusive rocks are enriched in large ion lithophile elements and depleted in high field strength elements relative to N-MORB, with low Nb/U (1.53-5.27) and high Ba/Nb (1.68-121) ratios, indicating that the primary magma was derived from partial melting of a metasomatized mantle source. The mafic-ultramafic rocks in the Northern Tianshan are characterized by lower Ca contents (b1000 ppm) in olivine, more depleted Nb and Ta, lower Nb/U ratios, and higher εΝd (t) than those of the Tarim mafic-ultramafic intrusive rocks and ocean island basalts (OIB). The range of εΝd (t) values of the mafic-ultramafic rocks in the Northern Tianshan over time suggests a greater role for upwelling asthenospheric mantle in the younger rocks. This implies that they were produced by interactions between metasomatized lithospheric mantle and depleted asthenospheric melts rather than a mantle plume. The linear distribution of Permian mafic-ultramafic intrusions along the Kangguer fault in the Northern Tianshan suggests that slab breakoff played a key role in the genesis of the mantle-derived magma in a syn-collisional setting.
The Keketale Pb-Zn deposit is located in the Devonian volcanic-sedimentary Maizi basin of the Alt... more The Keketale Pb-Zn deposit is located in the Devonian volcanic-sedimentary Maizi basin of the Altay orogenic belt. The mineralization at Keketale is hosted in marbles and deformed volcanic tuffs and biotite-garnet-chlorite schists, folded into a series of overturned synclines formed in multiple deformation events. Keketale contains economic amounts of Pb (0.89 Mt @ 1.51 wt.%), Zn (1.94 Mt @ 3.16 wt.%) and Ag (650 t @ 40 g/t). Detailed petrographic studies have defined two main generations of sulfide development. The banded pyrite of the early Stage A is commonly stratiform, with minor galena, sphalerite and chalcopyrite. Stage B is characterized by a large amount of polymetallic sulfides including pyrrhotite, chalcopyrite, sphalerite and galena, with minor pyrite hosted in quartz veins. Three types of fluid inclusions (FIs), including mixed carbonic-aqueous (C-type), pure carbonic (PC-type) and aqueous (W-type), have been recognized in quartz of stage B. The C-type FIs have homogenization temperatures of 150-326°C and salinities of 0.2-16.6 wt.% NaCl equivalent. The PC-type FIs are dominated by CO 2 with minor CH 4 and N 2 and have initial ice-melting temperatures of −57.5 to −56.7°C, CO 2 homogenization temperatures of 11-14.1°C. The W-type primary FIs were completely homogenized at temperatures of 124-359°C with salinities of 5.0-14.6 wt.% NaCl equivalent. Such CO 2 -rich fluid inclusions are consistent with those discovered in orogenic-type deposits in the Altay area and elsewhere. Muscovite separates from the polymetallic quartz veinlets of stage B yield a well-defined 40 Ar/ 39 Ar isotopic plateau age of 259.33 ± 2.56 Ma, with an isochron age of 259.62 ± 2.65 Ma. This age is coeval with the closure of the Paleo-Asia Ocean and reactivation of the Ertix Fault system. LA-ICP-MS analyses of two generations of pyrite indicate that the banded pyrite of stage A is relatively depleted in metallic elements and contains low contents of Cu (0.39 ppm), Ag (0.20 ppm), Au (below the detection limits), Pb (17.43 ppm) and Zn (14.38 ppm); whereas the pyrite in quartz-polymetallic sulfide veinlets of the stage B is relatively rich in metallic elements, e.g., Cu (2.56 ppm), Ag (3.07 ppm), Au (0.01 ppm), Pb (1047 ppm) and Zn (1136 ppm). The trace amounts of Cu, Pb, Zn, Au and Ag are interpreted to have been initially locked in the lattice of type-A pyrite, and then liberated and precipitated as micromineral inclusions with type-B pyrite during subsequent metamorphism and deformation. Two key factors are considered vital to the formation of economic ores of the Keketale Pb-Zn deposit, namely the original Devonian banded pyrite formed in a VMS system and subsequent Permian deformation and metamorphic processes that liberated Cu, Pb, Zn, Au and Ag from the lattice of type-A pyrite to form galena, sphalerite and chalcopyrite with minor muscovite in quartz veinlets. The model provides a new interpretation of VMS Pb-Zn deposit occurring in back-arc basin environments followed by collision, and new insights into the unique regional Fe-Cu-Pb-Zn-Au mineralization in the Altay orogenic belt.
The Talate ore field is located in the Abagong polymetallic metallogenic belt of the Altay Orogen... more The Talate ore field is located in the Abagong polymetallic metallogenic belt of the Altay Orogen, NW China. Lenticular ore bodies occur in the Kangbutiebao Formation, a package of intermediate-felsic marine volcanic rocks and terrigenous clastic sedimentary-carbonate rocks. Skarn alteration (mainly garnet) is present in both ore and wall rocks, especially the carbonate rocks. The mineral assemblages and crosscutting relationships of veins allow the alteration and mineralization process to be divided into four stages. From early to late, these are the early skarn (E-skarn), the late skarn with quartz-magnetite veins (QM), the quartz-sulphide (QS) and the quartz-carbonate (QC) assemblages. Quartz crystals are important gangue minerals in the latter three stages, in which four distinct compositions of fluid inclusions are identified based on petrography, microthermometry and laser Raman microspectroscopy, namely aqueous inclusions (W-type), pure CO 2 inclusions (PC-type), CO 2 -rich inclusions (C-type) and daughter mineral-bearing inclusions (S-type). Microthermometric data and laser Raman analyses show that the quartz crystals from the QM stage contain all four inclusion types, with the W-type being predominant. Homogenization temperatures range between 271 and 426°C. The salinities of the W-and C-type fluid inclusions range from 0.5 to 22.4 wt.% NaCl eqv., whereas the S-type fluid inclusions in the QM stage range from 31 to 41 wt.% NaCl eqv. Daughter minerals in the fluid inclusions include halite, sylvite, pyrite and calcite. Quartz from the QS stage (main mineralization stage) contains the W-, C-and PC-type inclusions, which are homogenized at temperatures of 204-269°C, with salinities of 0.2-15.6 wt.% NaCl eqv. Only W-type fluid inclusions have been identified in the QC stage. These yielded homogenizing temperatures of 175-211°C and salinities of 1.1-9.9 wt.% NaCl eqv. The C-type fluid inclusions of the main (QS) mineralization stage yield trapping pressures of 107-171 MPa, corresponding to a depth of 4-6 km. The sulphur isotope values (À1.7‰ and À6.6‰) imply that the QS stage may not be directly associated with the early skarn (À7.4‰) and quartz-magnetite stages (À4.8‰ and À5.0‰), though the QS stage is probably dominated by magmatic-hydrothermal fluids. 40 Ar/ 39 Ar isotope plateau ages of 227.6 and 214.1 Ma for biotite separated from the QM and QS stages are significantly younger than the host Kangbutiebao Formation (ca. 410 Ma). The Talate Pb-Zn(-Fe) deposit is interpreted to be an unusual skarn-type system formed in a continental collision orogeny.
Please cite this article as: Wyman, D.A., Hollings, P., Conceição, R.V., Geochemistry and radioge... more Please cite this article as: Wyman, D.A., Hollings, P., Conceição, R.V., Geochemistry and radiogenic isotope characteristics of xenoliths in Archean diamondiferous lamprophyres: Implications for the Superior Province cratonic keel, LITHOS (2015),
The Baguio district, in the Central Cordillera of Northern Luzon, Philippines forms part of a mag... more The Baguio district, in the Central Cordillera of Northern Luzon, Philippines forms part of a magmatic arc associated with subduction of the South China Sea plate beneath the Philippines and Taiwan. The district contains porphyry-style copper, epithermal gold and skarn mineralisation associated with a series of Early Miocene to Late Pliocene volcanic and intrusive rocks that have calc-alkaline affinities. Detailed
High precision trace element data from ultramafic and mafic volcanic rocks from two units of the~... more High precision trace element data from ultramafic and mafic volcanic rocks from two units of the~3 Ga North Caribou greenstone belt in the northwestern Superior Province reveals new evidence for the contamination of early Archaean komatiites. Spinifex-textured komatiites (MgO=20−-27 wt.%) of the Opapimiskan-Markop unit are characterised by flat to moderately enriched light rare earth element (LREE) trace element patterns (La/Sm n =1-2) in conjunction with negative Nb and Ti anomalies (Nb/La pm =0.48-0.59; Ti/Ti*=0.6-0.8), consistent with contamination of a primary Munro-type Al-undepleted ultramafic melt by felsic material compositionally similar to Archaean tonalitic-trondhjemitic-granodioritic (TTG) suites. The trace element characteristics of these komatiites are distinct from both Proterozoic and Phanerozoic arc and rift picrites. Mg-tholeiites intimately associated with the komatiites display variable rare earth elements (REE) (La/Sm n =0.8-1.5) and Nb and Ti anomalies also consistent with variable degrees of contamination (Nb/La pm =0.58-0.98; Ti/Ti*=0.6-1.0). An intermediate suite of high-Mg andesites (54-60 wt.% SiO 2 ) associated with both the tholeiites and the komatiites can be derived by fractional crystallisation of a melt with the trace element characteristics of the most contaminated komatiites. Compositionally uniform Mgto Fe-tholeiites of the South Rim unit are believed to overlie the Opapimiskan-Markop unit, possibly in stratigraphic contact. They are characterised by flat trace element patterns (La/Sm n =0.9-1.0), are uncontaminated, and comparable with modern day oceanic plateaux, such as Ontong Java. The two units likely represent the eruptive products of a single mantle plume that entrained tholeiitic melts from the upper mantle before impinging upon the Archaean crust at~3 Ga.
Archaean greenstone belts from the northern Superior Province, ranging in age from 2.9 to 3.0 Ga,... more Archaean greenstone belts from the northern Superior Province, ranging in age from 2.9 to 3.0 Ga, comprise an association of komatiite-tholeiite sequences intercalated with arc-related felsic volcanic rocks. These belts are distinct from their southern counterparts in at least four ways: (1) several of the komatiite sequences are characterised by a compositional signature of contamination; (2) there is evidence for older crustal basement to some of the greenstone belts; (3) several of the komatiites possess positive peaks of Sc and V relative to HREE, and (4) they extend to greater ages than their southern counterparts.
Résumé : Des analyses complètes des éléments traces de roches volcaniques mafiques et felsiques p... more Résumé : Des analyses complètes des éléments traces de roches volcaniques mafiques et felsiques provenant de la ceinture de roches vertes Meen-Dempster, 2,85–2,74 Ga, montrent une grande diversité de composition. L'assemblage Kaminiskag,2,85 Ga, est dominé par une tholéiite ...
... Mike Easton, Pete Hollings, and Wally Rayner ... Hart and MacDonald (2007) summarize the resu... more ... Mike Easton, Pete Hollings, and Wally Rayner ... Hart and MacDonald (2007) summarize the results arising from 1:50000-scale bedrock mapping conducted west of Lake Nipigon in 2003 and 2004 (Hart and Magyarosi 2004; MacDonald 2004; Hart 2005a; MacDonald et al. 2005). ...
During a five week period, 19 caves were explored by a team of four cavers comprising the 1994 Me... more During a five week period, 19 caves were explored by a team of four cavers comprising the 1994 Mendip Caving Group (MCG) expedition to Belize. Six sizable caves were identified in the Cretaceous limestone, west of the Maya Mountains, and surveyed a total length of 2.5 km. Time spent in the field is broken down so as to show both the advantages and disadvantages of a small-scale expedition. Suggestions are made as to how future groups could benefit from the experiences of the expedition with regard to conducting significant research with a small team. The MCG expedition is compared to other larger expeditions, with the results showing that lightweight expeditions are more easily financed and organized than larger expeditions; however, they may not be suitable if detailed scientific studies are intended.
The Caixiashan giant carbonate-hosted Zn-Pb deposit (~131 Mt@ 3.95% Zn + Pb) formed by replacemen... more The Caixiashan giant carbonate-hosted Zn-Pb deposit (~131 Mt@ 3.95% Zn + Pb) formed by replacement of dolomitized marble, with stratiform massive and breccia bodies is located near the base of the Proterozoic Kawabulake Group limestone and marble. It is one of the largest carbonated-hosted massive sulfides Zn-Pb ore deposits in Northwest China to have been discovered in recent years. Abundant pyrite occurs in dolomitized marble, along fractures in dolomitized clasts in the host rocks and filling cracks in the host rock. Locally, colloform or framboidal pyrites are observed in the early period and sometimes replaced by the later sphalerite. The sulfide assemblage of the main ore stage is characterized by massive or disseminated sphalerite and galena, with less pyrite than the earlier stage, and minor pyrrhotite. Galena occurs as small veins cutting the early-formed sphalerite. Dolomite and calcite are the main gangue minerals that coprecipitated with these sulfides. Tremolite and quartz alteration commonly overprints the orebodies. According to the crosscutting relationships and the different mineral associations within the host rocks and ore bodies, three stages are recognized at Caixiashan, i.e., syn-sedimentary pyrite (stage I), pyrite alteration, sphalerite-carbonate and galena-pyrite-carbonate (stage II-1, stage II-2 and stage II-3, respectively) and magmatic/metamorphic reworking (stage III). Calcite and quartz crystals are important host minerals among the three hypogene stages (stages I-III, although quartz mainly occurred in stage III). Stage I contains only aqueous inclusions (W-type), which were homogenized from 110 to 236°C (main range of 138-198°C and average at 168°C; main range = average ± σ) and the salinities are from 0.5 to 16.5 (main range of 5.1-15.1 with average of 10.1) wt.% NaCl eqv. In the pyrite alteration of stage II-1 the W-type fluid inclusions homogenized from 175 to 260°C (main range of 210-260 with average of 235) and the salinities range from 8.5 to 22.4 (main range of 16.7-20.1 with average of 18.4) wt.% NaCl eqv. In the main Zn-Pb mineralization stage (stage II-2-3), four types of fluid inclusions were identified an aqueous phase (W-type), a pure carbon phase (PC-type), a carbon phase containing (C-type) and mineral bearing inclusions (S-type). The W-type fluid inclusions of stage II-2-3 homogenized at 210 to 370°C (main range of 253-323 and average at 270) and the salinities range from 5.9 to 23.1 (main range of 13.3-20.3 with average at 16.8) wt.% NaCl eqv.; C-type homogenized at 237°C to 371°C and the salinities range from 6.4-19.7 wt.% NaCl eqv.; S-type fluid inclusions homogenized at 211 to 350°C and daughter minerals melted between 340 and 374°C during heating, indicating a salinity range of 42 to 44 wt.% NaCl eqv. PC-type fluid inclusions with homogenization temperatures of CO 2 phase show large variation from 7.4°C to 21.2°C. Laser Raman analyses show that CH 4 , CO 2 and SO 4 2 − coexist in the main mineralization stage fluids. The magmatic/metamorphic reworking stage only contains W-type fluid inclusions which yield homogenized between 220 and 360°C (main range of 251-325 and average at 288), with salinities ranging from 1.7 to 23.0 (main range of 14.3-20.0 and average at 18.8) wt.% NaCl eqv. The textural features, mineral assemblages and fluid geochemistry suggest that the Zn-Pb ores were formed through hydrothermal convection of hot marine waters along the faults and fractures resulting in metal (Zn, Ore Geology Reviews 72 (2015) [355][356][357][358][359][360][361][362][363][364][365][366][367][368][369][370][371][372] Pb and Fe) enriched stratiform orebodies. Subsequent rapid precipitation of sulfides was triggered by sulfate (SO 4 2− ) thermal reduction with the CH 4 preserved in sedimentary rocks and early stage I pyrite bodies. This process occurred at moderate temperatures (ca. 270°C). Higher-temperature magmatic hydrothermal alteration overprinted the orebodies, but only provided a minor contribution to the mineralization.
The Huangshan mafic-ultramafic intrusion hosts a large Ni-Cu sulfide deposit and is situated in t... more The Huangshan mafic-ultramafic intrusion hosts a large Ni-Cu sulfide deposit and is situated in the Northern Tianshan at the southern margin of the Central Asian Orogenic Belt (CAOB). The Early Permian intrusion consists of lherzolite, websterite, gabbronorite, gabbro and diorite. The Huangshan deposit contains~80.4 Mt of ore grading 0.54 wt.% Ni and 0.3 wt.% Cu and is the second largest magmatic sulfide deposit in Northern Xinjiang, China. The Huangshan intrusive rocks are enriched in large ion lithophile elements and depleted in high field strength elements relative to N-MORB, with low Nb/U (1.53-5.27) and high Ba/Nb (1.68-121) ratios, indicating that the primary magma was derived from partial melting of a metasomatized mantle source. The mafic-ultramafic rocks in the Northern Tianshan are characterized by lower Ca contents (b1000 ppm) in olivine, more depleted Nb and Ta, lower Nb/U ratios, and higher εΝd (t) than those of the Tarim mafic-ultramafic intrusive rocks and ocean island basalts (OIB). The range of εΝd (t) values of the mafic-ultramafic rocks in the Northern Tianshan over time suggests a greater role for upwelling asthenospheric mantle in the younger rocks. This implies that they were produced by interactions between metasomatized lithospheric mantle and depleted asthenospheric melts rather than a mantle plume. The linear distribution of Permian mafic-ultramafic intrusions along the Kangguer fault in the Northern Tianshan suggests that slab breakoff played a key role in the genesis of the mantle-derived magma in a syn-collisional setting.
The Keketale Pb-Zn deposit is located in the Devonian volcanic-sedimentary Maizi basin of the Alt... more The Keketale Pb-Zn deposit is located in the Devonian volcanic-sedimentary Maizi basin of the Altay orogenic belt. The mineralization at Keketale is hosted in marbles and deformed volcanic tuffs and biotite-garnet-chlorite schists, folded into a series of overturned synclines formed in multiple deformation events. Keketale contains economic amounts of Pb (0.89 Mt @ 1.51 wt.%), Zn (1.94 Mt @ 3.16 wt.%) and Ag (650 t @ 40 g/t). Detailed petrographic studies have defined two main generations of sulfide development. The banded pyrite of the early Stage A is commonly stratiform, with minor galena, sphalerite and chalcopyrite. Stage B is characterized by a large amount of polymetallic sulfides including pyrrhotite, chalcopyrite, sphalerite and galena, with minor pyrite hosted in quartz veins. Three types of fluid inclusions (FIs), including mixed carbonic-aqueous (C-type), pure carbonic (PC-type) and aqueous (W-type), have been recognized in quartz of stage B. The C-type FIs have homogenization temperatures of 150-326°C and salinities of 0.2-16.6 wt.% NaCl equivalent. The PC-type FIs are dominated by CO 2 with minor CH 4 and N 2 and have initial ice-melting temperatures of −57.5 to −56.7°C, CO 2 homogenization temperatures of 11-14.1°C. The W-type primary FIs were completely homogenized at temperatures of 124-359°C with salinities of 5.0-14.6 wt.% NaCl equivalent. Such CO 2 -rich fluid inclusions are consistent with those discovered in orogenic-type deposits in the Altay area and elsewhere. Muscovite separates from the polymetallic quartz veinlets of stage B yield a well-defined 40 Ar/ 39 Ar isotopic plateau age of 259.33 ± 2.56 Ma, with an isochron age of 259.62 ± 2.65 Ma. This age is coeval with the closure of the Paleo-Asia Ocean and reactivation of the Ertix Fault system. LA-ICP-MS analyses of two generations of pyrite indicate that the banded pyrite of stage A is relatively depleted in metallic elements and contains low contents of Cu (0.39 ppm), Ag (0.20 ppm), Au (below the detection limits), Pb (17.43 ppm) and Zn (14.38 ppm); whereas the pyrite in quartz-polymetallic sulfide veinlets of the stage B is relatively rich in metallic elements, e.g., Cu (2.56 ppm), Ag (3.07 ppm), Au (0.01 ppm), Pb (1047 ppm) and Zn (1136 ppm). The trace amounts of Cu, Pb, Zn, Au and Ag are interpreted to have been initially locked in the lattice of type-A pyrite, and then liberated and precipitated as micromineral inclusions with type-B pyrite during subsequent metamorphism and deformation. Two key factors are considered vital to the formation of economic ores of the Keketale Pb-Zn deposit, namely the original Devonian banded pyrite formed in a VMS system and subsequent Permian deformation and metamorphic processes that liberated Cu, Pb, Zn, Au and Ag from the lattice of type-A pyrite to form galena, sphalerite and chalcopyrite with minor muscovite in quartz veinlets. The model provides a new interpretation of VMS Pb-Zn deposit occurring in back-arc basin environments followed by collision, and new insights into the unique regional Fe-Cu-Pb-Zn-Au mineralization in the Altay orogenic belt.
The Talate ore field is located in the Abagong polymetallic metallogenic belt of the Altay Orogen... more The Talate ore field is located in the Abagong polymetallic metallogenic belt of the Altay Orogen, NW China. Lenticular ore bodies occur in the Kangbutiebao Formation, a package of intermediate-felsic marine volcanic rocks and terrigenous clastic sedimentary-carbonate rocks. Skarn alteration (mainly garnet) is present in both ore and wall rocks, especially the carbonate rocks. The mineral assemblages and crosscutting relationships of veins allow the alteration and mineralization process to be divided into four stages. From early to late, these are the early skarn (E-skarn), the late skarn with quartz-magnetite veins (QM), the quartz-sulphide (QS) and the quartz-carbonate (QC) assemblages. Quartz crystals are important gangue minerals in the latter three stages, in which four distinct compositions of fluid inclusions are identified based on petrography, microthermometry and laser Raman microspectroscopy, namely aqueous inclusions (W-type), pure CO 2 inclusions (PC-type), CO 2 -rich inclusions (C-type) and daughter mineral-bearing inclusions (S-type). Microthermometric data and laser Raman analyses show that the quartz crystals from the QM stage contain all four inclusion types, with the W-type being predominant. Homogenization temperatures range between 271 and 426°C. The salinities of the W-and C-type fluid inclusions range from 0.5 to 22.4 wt.% NaCl eqv., whereas the S-type fluid inclusions in the QM stage range from 31 to 41 wt.% NaCl eqv. Daughter minerals in the fluid inclusions include halite, sylvite, pyrite and calcite. Quartz from the QS stage (main mineralization stage) contains the W-, C-and PC-type inclusions, which are homogenized at temperatures of 204-269°C, with salinities of 0.2-15.6 wt.% NaCl eqv. Only W-type fluid inclusions have been identified in the QC stage. These yielded homogenizing temperatures of 175-211°C and salinities of 1.1-9.9 wt.% NaCl eqv. The C-type fluid inclusions of the main (QS) mineralization stage yield trapping pressures of 107-171 MPa, corresponding to a depth of 4-6 km. The sulphur isotope values (À1.7‰ and À6.6‰) imply that the QS stage may not be directly associated with the early skarn (À7.4‰) and quartz-magnetite stages (À4.8‰ and À5.0‰), though the QS stage is probably dominated by magmatic-hydrothermal fluids. 40 Ar/ 39 Ar isotope plateau ages of 227.6 and 214.1 Ma for biotite separated from the QM and QS stages are significantly younger than the host Kangbutiebao Formation (ca. 410 Ma). The Talate Pb-Zn(-Fe) deposit is interpreted to be an unusual skarn-type system formed in a continental collision orogeny.
Please cite this article as: Wyman, D.A., Hollings, P., Conceição, R.V., Geochemistry and radioge... more Please cite this article as: Wyman, D.A., Hollings, P., Conceição, R.V., Geochemistry and radiogenic isotope characteristics of xenoliths in Archean diamondiferous lamprophyres: Implications for the Superior Province cratonic keel, LITHOS (2015),
The Baguio district, in the Central Cordillera of Northern Luzon, Philippines forms part of a mag... more The Baguio district, in the Central Cordillera of Northern Luzon, Philippines forms part of a magmatic arc associated with subduction of the South China Sea plate beneath the Philippines and Taiwan. The district contains porphyry-style copper, epithermal gold and skarn mineralisation associated with a series of Early Miocene to Late Pliocene volcanic and intrusive rocks that have calc-alkaline affinities. Detailed
High precision trace element data from ultramafic and mafic volcanic rocks from two units of the~... more High precision trace element data from ultramafic and mafic volcanic rocks from two units of the~3 Ga North Caribou greenstone belt in the northwestern Superior Province reveals new evidence for the contamination of early Archaean komatiites. Spinifex-textured komatiites (MgO=20−-27 wt.%) of the Opapimiskan-Markop unit are characterised by flat to moderately enriched light rare earth element (LREE) trace element patterns (La/Sm n =1-2) in conjunction with negative Nb and Ti anomalies (Nb/La pm =0.48-0.59; Ti/Ti*=0.6-0.8), consistent with contamination of a primary Munro-type Al-undepleted ultramafic melt by felsic material compositionally similar to Archaean tonalitic-trondhjemitic-granodioritic (TTG) suites. The trace element characteristics of these komatiites are distinct from both Proterozoic and Phanerozoic arc and rift picrites. Mg-tholeiites intimately associated with the komatiites display variable rare earth elements (REE) (La/Sm n =0.8-1.5) and Nb and Ti anomalies also consistent with variable degrees of contamination (Nb/La pm =0.58-0.98; Ti/Ti*=0.6-1.0). An intermediate suite of high-Mg andesites (54-60 wt.% SiO 2 ) associated with both the tholeiites and the komatiites can be derived by fractional crystallisation of a melt with the trace element characteristics of the most contaminated komatiites. Compositionally uniform Mgto Fe-tholeiites of the South Rim unit are believed to overlie the Opapimiskan-Markop unit, possibly in stratigraphic contact. They are characterised by flat trace element patterns (La/Sm n =0.9-1.0), are uncontaminated, and comparable with modern day oceanic plateaux, such as Ontong Java. The two units likely represent the eruptive products of a single mantle plume that entrained tholeiitic melts from the upper mantle before impinging upon the Archaean crust at~3 Ga.
Archaean greenstone belts from the northern Superior Province, ranging in age from 2.9 to 3.0 Ga,... more Archaean greenstone belts from the northern Superior Province, ranging in age from 2.9 to 3.0 Ga, comprise an association of komatiite-tholeiite sequences intercalated with arc-related felsic volcanic rocks. These belts are distinct from their southern counterparts in at least four ways: (1) several of the komatiite sequences are characterised by a compositional signature of contamination; (2) there is evidence for older crustal basement to some of the greenstone belts; (3) several of the komatiites possess positive peaks of Sc and V relative to HREE, and (4) they extend to greater ages than their southern counterparts.
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