Geology and Origin of the Dongping Alkalic‐Type Gold Deposit, Northern Hebei Province, People's Republic of China
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Abstract: The Dongping deposit, located near the center of the northern margin of the north China craton, is one of the largest gold deposits in China. It is spatially, temporally, and genetically associated with the shallowly‐emplaced Hercynian Shuiquan‐gou alkaline intrusive complex. The complex intrudes high‐grade metamorphic rocks of the Archean Sanggan Group along a deep‐seated fault zone within the north China craton. Four major ore bodies (Nos. 1, 2, 22, and 70), consisting mainly of a set of en echelon lenses and veins, have been delineated at the Dongping deposit. Hypogene hydrothermal activities can be divided into four periods from early to late including: (1) gold‐bearing K–feldspar–quartz stockworks and veins; (2) disseminated sulfide and gold zones; (3) gold‐bearing quartz veins, and (4) barren calcite‐quartz veins. Individual veins and stockwork systems can be traced along strike for 125 to 600 m and downdip for 100 to 600 m; they range from 0. 5 to 3 m in thickness. The mineralogical composition of the ore in the first three hypogene periods is relatively simple. It is composed of pyrite, galena, sphalerite, magnetite, specularite, chalcopyrite, native gold, electrum, calaverite, and altaite. Gangue minerals include K–feldspar, quartz, sericite, chlorite, epidote, albite, and calcite. Ore grade averages 6 g/t Au, but varies between 4. 14 and 22. 66 g/t Au. Gold is generally fine‐grained and not visible in hand specimen. Fluid inclusions in ore‐bearing quartz of periods 1, 2, and 3 are CO 2 –rich, variable salinity (2. 5–21 wt% equiv. NaCl), and have variable homogenization temperatures of 195° to 340°C. Quartz in the gold‐bearing K–feldspar–quartz stockworks (period 1), disseminated sulfide and gold zones (period 2), and the gold‐bearing quartz veins (period 3) has calculated δ 18 O H2O values between –1. 7 and 6. 9%, and δ values of fluid inclusion waters between –101 and –66%. All these isotope data of the ore‐forming fluids plot between the magmatic fluid field and the meteoric water line. Sulfide minerals disseminated in host rocks show positive δ 34 S values of 1. 9 to 3. 5%. Pyrite separates from he gold‐bearing K–feldspar–quartz stockworks and veins (period 1) have a δ 34 S range of –4. 3 to 0. 5%, whereas δ 34 S values of pyrite, chalcopyrite, galena, and sphalerite from the disseminated sul‐fide and gold zones (period 2) and the gold‐bearing quartz veins (period 3) vary from –5. 3 to –13. 4%. Gold ores are also characterized by relatively radiogenic lead isotope compositions compared to those of the alkaline syenite host rock. The data are interpreted as indicative of a mixing of lead from the alkaline intrusive complex with lead from Archean metamorphic rocks. The combined fluid inclusion measurements, sulfur, oxygen, hydrogen, and lead isotope data, and petrological observations indicate that the Dongping deposit was formed from the mixing of these magmatic fluids with meteoric waters. The deposit is, therefore, believed to be a product of Hercynian alkaline igneous processes within the north China craton.Keywords:
Hypogene
Sericite
Stockwork
Molybdenite
Arsenopyrite
Ore genesis
Abstract The Kapan mining district in the southernmost Lesser Caucasus is one of the few locations along the central Tethyan metallogenic belt where ore-forming processes were associated with magmatic arc growth during Jurassic Tethys subduction along the Eurasian margin. Three ore deposits of the Kapan district were investigated in this study: Centralni West, Centralni East, and Shahumyan. The ore deposits are hosted by Middle Jurassic andesitic to dacitic volcanic and volcaniclastic rocks of tholeiitic to transitional affinities below a late Oxfordian unconformity, which is covered by calc-alkaline to transitional Late Jurassic-Early Cretaceous volcanic rocks interlayered with sedimentary rocks. The mineralization consists of veins, subsidiary stockwork, and partial matrix replacement of breccia host rocks, with chalcopyrite, pyrite, tennantite-tetrahedrite, sphalerite, and galena as the main ore minerals. Centralni West is a dominantly Cu deposit, and its host rocks are altered to chlorite, carbonate, epidote, and sericite. At Centralni East, Au is associated with Cu, and the Shahumyan deposit is enriched in Pb and Zn as well as precious metals. Both deposits contain high-sulfidation mineral assemblages with enargite and luzonite. Dickite, sericite, and diaspore prevail in altered host rocks in the Centralni East deposit. At the Shahumyan deposit, phyllic to argillic alteration with sericite, quartz, pyrite, and dickite is dominant with polymetallic veins, and advanced argillic alteration with quartz-alunite ± kaolinite and dickite is locally developed. The lead isotope composition of sulfides and alunite (206Pb/204Pb = 18.17–18.32, 207Pb/204Pb = 15.57–15.61, 208Pb/204Pb = 38.17–38.41) indicates a common metal source for the three deposits and suggests that metals were derived from magmatic fluids that were exsolved upon crystallization of Middle Jurassic intrusive rocks or leached from Middle Jurassic country rocks. The δ18O values of hydrothermal quartz (8.3–16.4‰) and the δ34S values of sulfides (2.0–6.5‰) reveal a dominantly magmatic source at all three deposits. Combined oxygen, carbon, and strontium isotope compositions of hydrothermal calcite (δ18O = 7.7–15.4‰, δ13C = −3.4−+0.7‰, 87Sr/86Sr = 0.70537–0.70586) support mixing of magmatic-derived fluids with seawater during the last stages of ore formation at Shahumyan and Centralni West. 40Ar/39Ar dating of hydrothermal muscovite at Centralni West and of magmatic-hydrothermal alunite at Shahumyan yield, respectively, a robust plateau age of 161.78 ± 0.79 Ma and a disturbed plateau age of 156.14 ± 0.79 Ma. Re-Os dating of pyrite from the Centralni East deposit yields an isochron age of 144.7 ± 4.2 Ma and a weighted average age of the model dates of 146.2 ± 3.4 Ma, which are younger than the age of the immediate host rocks. Two different models are offered, depending on the reliability attributed to the disturbed 40Ar/39Ar alunite age and the young Re-Os age. The preferred interpretation is that the Centralni West Cu deposit is a volcanogenic massive sulfide deposit and the Shahumyan and Centralni East deposits are parts of porphyryepithermal systems, with the three deposits being broadly coeval or formed within a short time interval in a nascent magmatic arc setting, before the late Oxfordian. Alternatively, but less likely, the three deposits could represent different mineralization styles successively emplaced during evolution and growth of a magmatic arc during a longer time frame between the Middle and Late Jurassic.
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Argillic alteration
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Breccia
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Sericite
Hypogene
Stockwork
Actinolite
Breccia
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The Talnikovoye ore field where previous academic research and exploration work revealed porphyry copper mineralization is described. Our data show that mineralization is confined to the intrusions of Turonian granodiorite and quartz diorite (91 Ma, U-Pb metohod), as well as the accompanying hydrothermal-explosive breccias. Biotite-epidote-chlorite propylites are widespread within the ore field; in the southern part, phyllic alteration is superimposed on the halo of K-feldspar alteration. The ore occurs in zones of intense quartz, chlorite-epidote-quartz (with chalcopyrite and molybdenite), sulfide-potassium feldspar-quartz (with chalcopyrite and bornite), and sulfide-quartz-sericite (with chalcopyrite) stockwork veining with copper-molybdenum mineralization. They are characterized by moderate concentrations of Cu (0.1–0.3 %, reaching 1.1 %) and Mo (up to 0.1 %), low concentrations of Au (up to 0.1 g/t) and Ag (up to 2.6 g/t) and have a Cu-Mo-(Au, Ag, Pb, Zn, Sb, As) geochemical signature. Fluid inclusion data suggest the formation of mineralized veinlet quartz during the magmatic-hydrothermal transition (430–150 °С) with solutions at high (50 wt % NaCl equiv.), medium and low concentration (5–18.9 wt % NaCl equiv.) involved under the cooling-dilution scenario. Values of the main geochemical indicators, such as Cu/Mo (30–60) and Cu/Au (> 1 × 105) ratios allowed us to assign the Tal’nikovoye ore field to the porphyry copper-molybdenum type characteristic of continental-margin volcano-plutonic belts formed at the mafic island-arc basement. The geochemical parameters of porphyry granitoids indicate their formation in a setting of subduction-to-transform plate boundary transition.
Molybdenite
Sericite
Hypogene
Stockwork
Bornite
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Stockwork
Hypogene
Bornite
Actinolite
Metasomatism
Polymetallic replacement deposit
Ore genesis
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Argillic alteration
Sericite
Hypogene
Stockwork
Alunite
Molybdenite
Marcasite
Anhydrite
Arsenopyrite
Breccia
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Abstract The Japón, Tailandia and China Sur deposits in the Pelusa mineralized area correspond to a hematite‐dominant IOCG clan within the coastal Cordillera in the Antofagasta Region, Northern Chile, and their mineralization occurs in basaltic to andesitic volcanic rocks of the Jurassic La Negra Formation. In addition to geological and mineralogical descriptions, bulk chemistry of the host rocks, microthermometric and sulfur isotropic analyses were performed to elucidate ore‐forming characteristics of the three orebodies. Chemical data of the host rocks indicate a subalkaline calc‐alkaline affinity with enrichment of the incompatible LILEs, displaying a typical pattern of igneous rocks formed in subduction zones as a general characteristic of the Jurassic‐Lower Cretaceous magmatic arc. Chalcopyrite is the predominant hypogene copper mineral, that variously occurs as veinlets, disseminations and breccia matrix. Fluid inclusions data indicate formation temperatures of the hypogene mineralization ranging mostly from 186 to 377°C, with a high‐salinity range of 30.1 and 45.0 wt% NaCl. The sulfur isotopic ratios (δ 34 S CDT ) of pyrite and chalcopyrite present a narrow range of values from −10.6 to −7.5‰. The negative values in the limited range imply that sulfide minerals of the Pelusa area were formed under a relatively oxidizing and/or neutral pH condition, compared with other Chilean IOCG deposits.
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Breccia
Felsic
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The Copiapo GV area of northern-central Chile is situated in the transition zone between a Mesozoic iron oxide copper-gold(IOCG) deposit and a porphyry copper deposit.The intrusive rocks mainly consist of calc-alkaline,medium to coarse grained gabbro diorite,diorite,diorite porphyry,biotite granite,porphyritic granite and monzonite.These rocks are classified into the category of calc-alkaline,I-type and magnetite types,which is derived from the upper mantle.The assemblage of the intrusive rocks is interpreted to be formed at the subduction zone of oceanic crust during conversion from partially expansion to extrusion.As a consequence,the Mesozoic back-arc basin closed up and uplifted rapidly.The magma intruded mainly in the period of Late Cretaceous-Paleocene(about 65-54 Ma).The magmatic activities of different periods created a number of hydrothermal centeres and developed horizonal alteration zones and vein-type alteration-mineralization zones.On surface argilization-chlorite alteration,porous and silicified stockwork,and Au-Ag bearing Fe-Mn carbonate stockwork well developed.The widely extensive alteration zones contain gold,silver poly-metallic veins,which may indicate that the area could develop some epithermal Au-Ag poly-metallic deposits.These phenomena may present the potential of occurrence of IOCG mineralization or porphyry copper-gold mineralisation in deep area.Further study of alteration and mineralization should be strengthen,which will create a guideline of exploration for the deep-buried deposits in the future.
Stockwork
Diorite
Porphyritic
Quartz monzonite
Hypogene
Felsic
Mesothermal
Sericite
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Hypogene
Actinolite
Metasomatism
Ore genesis
Polymetallic replacement deposit
Bornite
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