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Magmatic Water (magmatic + water)
Selected AbstractsReactive flow of mixed CO2,H2O fluid and progress of calc-silicate reactions in contact metamorphic aureoles: insights from two-dimensional numerical modellingJOURNAL OF METAMORPHIC GEOLOGY, Issue 7 2003X. Cui Abstract Previous models of hydrodynamics in contact metamorphic aureoles assumed flow of aqueous fluids, whereas CO2 and other species are also common fluid components in contact metamorphic aureoles. We investigated flow of mixed CO2,H2O fluid and kinetically controlled progress of calc-silicate reactions using a two-dimensional, finite-element model constrained by the geological relations in the Notch Peak aureole, Utah. Results show that CO2 strongly affects fluid-flow patterns in contact aureoles. Infiltration of magmatic water into a homogeneous aureole containing CO2,H2O sedimentary fluid facilitates upward, thermally driven flow in the inner aureole and causes downward flow of the relatively dense CO2 -poor fluid in the outer aureole. Metamorphic CO2 -rich fluid tends to promote upward flow in the inner aureole and the progress of devolatilization reactions causes local fluid expulsion at reacting fronts. We also tracked the temporal evolution of P-T-XCO2conditions of calc-silicate reactions. The progress of low- to medium-grade (phlogopite- to diopside-forming) reactions is mainly driven by heat as the CO2 concentration and fluid pressure and temperature increase simultaneously. In contrast, the progress of the high-grade wollastonite-forming reaction is mainly driven by infiltration of chemically out-of-equilibrium, CO2 -poor fluid during late-stage heating and early cooling of the inner aureole and thus it is significantly enhanced when magmatic water is involved. CO2 -rich fluid dominates in the inner aureole during early heating, whereas CO2 -poor fluid prevails at or after peak temperature is reached. Low-grade metamorphic rocks are predicted to record the presence of CO2 -rich fluid, and high-grade rocks reflect the presence of CO2 -poor fluid, consistent with geological observations in many calc-silicate aureoles. The distribution of mineral assemblages predicted by our model matches those observed in the Notch Peak aureole. [source] Genesis and Age Constraints on Gold Deposits of the Daerae Mine, Sangju Area, Central-Northern Sobaegsan Massif, KoreaRESOURCE GEOLOGY, Issue 3 2001Seong, Taek YUN Abstract: Gold mineralization of the Daerae mine represents the first recognized example of the Jurassic gold mineralization in the Sangju area, Korea. It occurs as a single stage of quartz veins that fill fault fractures in Precambrian gneiss of the central-northern Sobaegsan Massif. The mineralogical characteristics of quartz veins, such as the simple mineralogy and relatively gold-rich (65,72 atomic % Au) nature of electrum, as well as the CO2,rich and low salinity nature of fluid inclusions, are consistent with the ,mesothermal-type' gold deposits previously recognized in the Youngdong area (about 50 km southwest of the Sangju area). Ore fluids were evolved mainly through CO2 immiscibility at temperatures between about 250 and 325 C. Vein sulfides characteristically have negative sulfur isotopic values (,1.9 to +0.2 %), which have been very rarely reported in South Korea, and possibly indicate the derivation of sulfur from an ilmenite-series granite melt. The calculated O and H isotopic compositions of hydrothermal fluids at Daerae (,18Owater = +5.2 to +5.9 %; ,Dwater = ,59 to ,67 %) are very similar to those from the Youngdong area, and indicate the important role of magmatic water in gold mineralization. The 40Ar,39Ar age dating of a pure alteration sericite sample yields a high-temperature plateau age of 188.3 0.1 Ma, indicating an early Jurassic age for the gold mineralization at Daerae. The lower temperature Ar-Ar plateau defines an age of 158.4 2.0 Ma (middle Jurassic), interpreted as reset by a subsequent thermal effect after quartz vein formation. The younger plateau age is the same as the previously reported K-Ar ages (145,171 Ma) for the other ,mesothermal,type' gold deposits in the Youngdong and Jungwon areas, Korea, which are too young in view of the new Jurassic Ar-Ar plateau age (around 188 Ma). [source] Genetic Environment of the Intrusion-related Yuryang Au-Te Deposit in the Cheonan Metallogenic Province, KoreaRESOURCE GEOLOGY, Issue 2 2006Sang Joon Pak Abstract. The Yuryang gold deposit, comprising a Te-bearing Au-Ag vein mineralization, is located in the Cheonan area of the Republic of Korea. The deposit is hosted in Precambrian gneiss and closely related to pegmatite. The mineralized veins display massive quartz textures, with weak alteration adjacent to the veins. The ore mineralization is simple, with a low Ag/Au ratio of 1.5:1, due to the paucity of Ag-phases. Ore mineralization took place in two different mineral assemblages with paragenetic time; early Fe-sulfide mineralization and late Fe-sulfide and Au-Te mineralization. The early Fe-sulfide mineralization (pyrite + sphalerite) occurred typically along the vein margins, and the subsequent Au-Te mineralization is characterized by fracture fillings of galena, sphalerite, pyrrhotite, Te-bearing minerals (petzite, altaite, hessite and Bi-Te mineral) and electrum. Fluid inclusions characteristically contain CO2 and can be classified into four types (Ia, Ib, IIa and IIb) according to the phase behavior. The pressure corrected temperatures (,500d,C) indicate that the deposit was formed at a distinctively high temperature from fluids with moderate to low salinity (<12 wt% equiv. NaCl) and CH4 (1,22 mole %). The sphalerite geo-barometry yield an estimated pressure about 3.5 ,2.1 kbar. The dominant ore-deposition mechanisms were CO2 effervescence and concomitant H2S volatilization, which triggered sulfidation and gold mineralization. The measured and calculated isotopic compositions of fluids (,18OH2O = 10.3 to 12.4 %o; ,DH2O = -52 to -77 %o) may indicate that the gold deposition originated from S-type magmatic waters. The physicochemical conditions observed in the Yuryang gold deposit indicate that the Jurassic gold deposits in the Cheonan area, including the Yuryang gold deposit are compatible with deposition of the intrusion-related Au-Te veins from deeply sourced fluids generated by the late Jurassic Daebo magmatism. [source] Geology and Genesis of the Superlarge Jinchang Gold Deposit, NE ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 4 2008JIA Guozhi Abstract The superlarge Jinchang gold deposit is located in the joint area between the Taipingling uplift and the Laoheishan depression of the Xingkai Block in both eastern Jilin and eastern Heilongjiang Province. Wall rocks of the gold deposits are the Neoproterozoic Huangsong Group of metamorphic rocks. Yanshanian magmatism in this region can be divided into 5 phases, the diorite, the graphic granite, the granite, the granite porphyry and the diorite porphyrite, which resulted in the magmatic domes and cryptoexplosive breecia chimney followed by large-scale hydrothermal alteration. Gold mineralization is closely related to the fourth and fifth phase of magmatism. According to the occurrences, gold ores can be subdivided into auriferous pyritized quartz vein, auriferous quartz-pyrite vein, auriferous polymetallic sulfide quartz vein and auriferous pyritized calcite vein. The ages of the gold deposit are ranging from 122.53 to 119.40 Ma. The ore bodies were controlled by a uniform tectono-magmatic hydrothermal alteration system that the ore-forming materials were deep derived from and the ore-forming fluids were dominated by magmatic waters with addition of some atmospheric water in the later phase of mineralization. Gold mineralization took place in an environment of medium to high temperatures and medium pressures. Ore-forming fluids were the K+ -Na+ -Ca2+ -Cl, -SO42- type and characterized by medium salinity or a slightly higher, weak alkaline and weak reductive. Au in the ore-forming fluids was transported as complexes of [Au (HS)2],, [AuCl2],, [Au(CO2)], and [Au(HCO3)2],. Along with the decline of temperatures and pressures, the ore-forming fluids varied from acidic to weak acidic and then to weak alkaline, which resulted in the dissociation of the complex and finally the precipitation of the gold. [source] | ||||||||||