DISCOVERY AND THE IMPLICATION OF A HYDROTHERMAL-METASOMATIC SKARN DEPOSIT IN GANGDISE TECTONIC ZONE,TIBET

DISCOVERY AND THE IMPLICATION OF A HYDROTHERMAL-METASOMATIC SKARN DEPOSIT IN GANGDISE TECTONIC ZONE,TIBET     

利用钾长石粉体合成雪硅钙石的实验研究

以氧化钙为反应物料,在200～250℃的水热反应条件下分解钾长石。实验研究了在不同的Ca/(Si Al)摩尔比、水固比、反应温度和反应时间条件下,钾长石中K2O的溶出率和固相的物相变化。结果表明,液相中K2O的溶出率为40%～87%,固相反应产物为结晶良好雪硅钙石晶体。采用化学分析、XRD、SEM、DSC_TG和BET等方法对合成的雪硅钙石粉体进行了表征,结果表明,合成的雪硅钙石粉体是由长5～10μm、宽100～200nm、厚度为49～50nm的薄片纤维晶体交织成的直径为30～40μm的空心球形团聚体,耐火温度高于650℃,是制备硅酸钙保温材料的良好原料。     

河南省嵩县大坪银-铅-锌多金属矿床地质特征及找矿标志

通过工作实践认为，大坪银-铅-锌多金属矿床是火山喷流沉积一后期热液叠加改造富集的块状硫化物多金属矿床。区域上NWW-SEE向晚元古-早古生代形成的裂谷型二郎坪蛇绿岩套是本区找矿的最佳区段，具四个含矿层位。矿化、矿石、矿物、元素等成矿作用要素具明显分带特征，并与火山作用及喷流作用有关。区域构造、同生断裂及岩浆作用为重要控矿条件，而硫化物层、重晶石层、硅质岩是银-铅-锌矿床的重要找矿标志。     

Sulfur isotopic effects in the disproportionation reaction of sulfur dioxide in hydrothermal fluids: implications for the δS variations of dissolved bisulfate and elemental sulfur from active crater lakes

Sulfur isotope effects during the SO₂ disproportionation reaction to form elemental sulfur (3SO₂+3H₂O→2HSO₄⁻+S+2H⁺) at 200–330°C and saturated water vapor pressures were experimentally determined. Initially, a large kinetic isotopic fractionation takes place between HSO₄⁻ and S, followed by a slow approach to equilibrium. The equilibrium fractionation factors, estimated from the longest run results, are expressed by 1000 ln α_HSO4⁻–S=6.21×10⁶/T²+3.62. The rates at which the initial kinetic fractionation factors approach the equilibrium ones were evaluated at the experimental conditions.δ³⁴S values of HSO₄⁻ and elemental sulfur were examined for active crater lakes including Noboribetsu and Niseko, (Hokkaido, Japan), Khloridnoe, Bannoe and Maly Semiachik (Kamchatka), Poás (Costa Rica), Ruapehu (New Zealand) and Kawah Ijen and Keli Mutu (Indonesia). Δ_HSO4⁻–S values are 28‰ for Keli Mutu, 26‰ for Kawah Ijen, 24‰ for Ruapehu, 23‰ for Poás, 22‰ for Maly Semiachik, 21‰ for Yugama, 13‰ for Bannoe, 9‰ for Niseko, 4‰ for Khloridonoe, and 0‰ for Noboribetsu, in the decreasing order. The SO₂ disproportionation reaction in the magmatic hydrothermal system below crater lakes where magmatic gases condense is responsible for high Δ_HSO4⁻–S values, whereas contribution of HSO₄⁻ produced through bacterial oxidation of reduced sulfur becomes progressively dominant for lakes with lower Δ_HSO4⁻–S values. Currently, Noboribetsu crater lake contains no HSO₄⁻ of magmatic origin. A 40-year period observation of δ³⁴S_HSO4⁻ and δ³⁴S_S values at Yugama indicated that the isotopic variations reflect changes in the supply rate of SO₂ to the magmatic hydrothermal system. This implies a possibility of volcano monitoring by continuous observation of δ³⁴S_HSO4⁻ values. The δ¹⁸O values of HSO₄⁻ and lake water from the studied lakes covary, indicating oxygen isotopic equilibration between them. The covariance gives strong evidence that lake water circulates through the sublimnic zone at temperatures of 140±30°C.     

A model for the magmatic–hydrothermal system at Mount Rainier,Washington, from seismic and geochemical observations

 Mount Rainier is one of the most seismically active volcanoes in the Cascade Range, with an average of one to two high-frequency volcano-tectonic (or VT) earthquakes occurring directly beneath the summit in a given month. Despite this level of seismicity, little is known about its cause. The VT earthquakes occur at a steady rate in several clusters below the inferred base of the Quaternary volcanic edifice. More than half of 18 focal mechanisms determined for these events are normal, and most stress axes deviate significantly from the regional stress field. We argue that these characteristics are most consistent with earthquakes in response to processes associated with circulation of fluids and magmatic gases within and below the base of the edifice.Circulation of these fluids and gases has weakened rock and reduced effective stress to the point that gravity-induced brittle fracture, due to the weight of the overlying edifice, can occur. Results from seismic tomography and rock, water, and gas geochemistry studies support this interpretation. We combine constraints from these studies into a model for the magmatic system that includes a large volume of hot rock (temperatures greater than the brittle–ductile transition) with small pockets of melt and/or hot fluids at depths of 8–18 km below the summit. We infer that fluids and heat from this volume reach the edifice via a narrow conduit, resulting in fumarolic activity at the summit, hydrothermal alteration of the edifice, and seismicity. Received: 10 February 1999 / Accepted: 26 June 1999     

Mitigation of asphaltics deposition during CO2 flood by enhancing CO2 solvency with chemical modifiers

CO₂ injected in the reservoir of McElroy Field, TX, for a CO₂ flood was in the supercritical state. Supercritical CO₂ fluid is capable of extracting light and intermediate hydrocarbons from rocks but is unable to extract heavy hydrocarbons and asphaltics. Therefore, plugging of asphaltics in reservoir rocks and a consequent reduction in injectivity and recovery may result when CO₂ only is used in enhanced oil recovery. By adding common solvents as chemical modifiers, the flooding fluid shows marked improvement in solvency for heavy components of crudes due to its increased density and polarity. Numerous supercritical CO₂ fluid extractions of dolomite rock from the Grayburg Formation containing known amount of spiked McElroy crude oil have been carried out to evaluate extraction efficiencies of CO₂ and CO₂ with chemical modifiers at various temperatures and pressures. All experiments show that extraction efficiency increases with increasing CO₂ pressure but decreases with increasing temperature. Addition of chemical modifiers to CO₂ also shows improved extraction efficiency and reduced asphaltic deposits. Under the pressure and temperature similar to McElroy reservoir conditions; chemically modified CO₂ yielded almost 3 times as much oil extracts as those in extractions with CO₂ only. It also reduced the asphaltics content in extracted rocks to nearly one half; indicating its potential for mitigating asphaltics plugging of formation rocks     

山东平邑卓家庄金矿金品位的分形结构特征及意义

卓家庄金矿为隐爆角砾岩型金矿床,主要矿石类型可分为４种：矿浆胶结隐爆角砾岩矿石、热液胶结隐爆角砾岩矿石、熔浆胶结隐爆角砾岩矿石、凝灰质胶结隐爆角砾岩矿石。金品位分形结构研究表明,该矿床具有多次分形结构及规律性变化特点,反映了多次矿化叠加的特点,并预示了深部矿化的存在。     

Fluid flow from pore pressure measurements off La Palma, Canary Islands

In situ subseafloor pore pressure results from the western flank of the island of La Palma, Canary Islands, are presented. The data obtained with a Pop Up Pore Pressure Instrument (PUPPI) provide constraints on the fluid circulation and its causes in a very special context: The sediment piles near an intraplate oceanic island built on the continental rise of the Northwest African Margin. The ambient pore pressures estimated from 2 to 4 days long record are negative in almost all cases with values, at depths of a few meters below sea floor, usually on the order of −10 to −70 Pa. Excess pore pressures develop only in the distal most areas. The permeabilities and compressibilities obtained respectively from the decay of the insertion pressures and the amplitude of the tidally induced pore pressure variations range between 2.5×10⁻¹⁸ and 6.6×10⁻¹⁶ m² and, 6.2×10⁻⁹ and 1.5×10⁻⁷ Pa⁻¹. According to these permeabilities fluid flow is estimated to be mostly downward and usually on the range between 0 and −0.3 mm y⁻¹. However, from the excess pore pressure profile a complex pattern of fluid circulation is inferred where horizontal fluid motion cannot be neglected. Horizontal flow is probably controlled by significant contrasts in the permeability of the different layers. The prevailing downward fluid flow is abnormal for a classical passive margin. We thus interpret these results as the superposition to the loss of fluids by sediment compaction (on the continental rise), of a large-scale flow system stimulated by thermal buoyancy (100 km wide) related to the volcanic activity on the island of La Palma.     

Formation of the Devonian Fengtai Hydrothermal Brine Basin and the Metallogeny of Gold and Lead-Zinc Mineralizations in Shaanxi

The study of the relationships between the hydrothermal sedimentary formations and the gold andlead-zinc mineralizations in the Devonian Fengtai basin in Shaanxi shows that there was a hydrothermal brine sedimentary event which was inserted into the normal sedimentary background from the late Middle Devonian to the early Late Devonian. This event is closely related to gold and lead-zinc mineralizations in this area.     

Uraniferous Black Shale and Related Uranium Mineralization Features in South China

: Black shales are marine sediments with argillaceous, silty and siliceous compositions and high contents of organic materials, disseminated pyrite and uranium. Uraniferous black shale has uranium content of more than 20 ppm.Black shales are widely distributed in 17 provinces or autonomous regions in northwestern and southern-central China. Their sedimentary ages are from the Sinian to the Tertiary and uraniferous black shales are mainly exposed in Yunnan, Guizhou, Sichuan, Hunan, Hubei, Jiangxi, and Zhejiang provinces and Guangxi Zhuang Autonomous Region and the economically significant uranium deposits associated with black shale occur in Hunan and Jiangxi provinces and Guangxi Zhuang Autonomous Region.Uranium mineralization associated with black shale has the following main features: (1) forming stratabound deposits; (2) controlled by structures such as interlayer and intersected faults and fractures; (3) associated with different ore-forming processes such as leaching and hydrothermal reworking; (4)