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991.
Gold ore-forming fluids of the Tanami region, Northern Australia 总被引:1,自引:0,他引:1
Fluid inclusion studies have been carried out on major gold deposits and prospects in the Tanami region to determine the compositions
of the associated fluids and the processes responsible for gold mineralization. Pre-ore, milky quartz veins contain only two-phase
aqueous inclusions with salinities ≤19 wt% NaCl eq. and homogenization temperatures that range from 110 to 410°C. In contrast,
the ore-bearing veins typically contain low to moderate salinity (<14 wt% NaCl eq.), H2O + CO2 ± CH4 ± N2-bearing fluids. The CO2-bearing inclusions coexist with two-phase aqueous inclusions that exhibit a wider range of salinities (≤21 wt% NaCl eq.).
Post-ore quartz and carbonate veins contain mainly two-phase aqueous inclusions, with a last generation of aqueous inclusions
being very CaCl2-rich. Salinities range from 7 to 33 wt% NaCl eq. and homogenization temperatures vary from 62 to 312°C. Gold deposits in
the Tanami region are hosted by carbonaceous or iron-rich sedimentary rocks and/or mafic rocks. They formed over a range of
depths at temperatures from 200 to 430°C. The Groundrush deposit formed at the greatest temperatures and depths (260–430°C
and ≤11 km), whereas deposits in the Tanami goldfield formed at the lowest temperatures (≥200°C) and at the shallowest depths
(1.5–5.6 km). There is also evidence in the Tanami goldfield for late-stage isothermal mixing with higher salinity (≤21 wt%
NaCl eq.) fluids at temperatures between 100 and 200°C. Other deposits (e.g., The Granites, Callie, and Coyote) formed at
intermediate depths and at temperatures ranging from 240 to 360°C. All ore fluids contained CO2 ± N2 ± CH4, with the more deeply formed deposits being enriched in CH4 and higher level deposits being enriched in CO2. Fluids from deposits hosted mainly by sedimentary rocks generally contained appreciable quantities of N2. The one exception is the Tanami goldfield, where the quartz veins were dominated by aqueous inclusions with rare CO2-bearing inclusions. Calculated δ
18O values for the ore fluids range from 3.8 to 8.5‰ and the corresponding δD values range from −89 to −37‰. Measured δ
13C values from CO2 extracted from fluid inclusions ranged from −5.1 to −8.4‰. These data indicate a magmatic or mixed magmatic/metamorphic source
for the ore fluids in the Tanami region. Interpretation of the fluid inclusion, alteration, and structural data suggests that
mineralization may have occurred via a number of processes. Gold occurs in veins associated with brittle fracturing and other
dilational structures, but in the larger deposits, there is also an association with iron-rich rocks or carbonaceous sediments,
suggesting that both structural and chemical controls are important. The major mineralization process appears to be boiling/effervescence
of a gas-rich fluid, which leads to partitioning of H2S into the vapor phase resulting in gold precipitation. However, some deposits also show evidence of desulfidation by fluid–rock
interaction and/or reduction of the ore-fluid by fluid mixing. These latter processes are generally more prevalent in the
higher crustal-level deposits. 相似文献
992.
993.
Anomaly analysis is used for various geophysics applications such as determination of geophysical structure's location and
border detections. Besides the classical geophysical techniques, artificial intelligence based image processing algorithms
have been found attractive for geophysical anomaly analysis. Recently, cellular neural networks (CNN) have been applied to
geophysical data and satisfactory results are reported. CNN provides fast and parallel computational capability for geophysical
image processing applications due to its filtering structure. The behavior of CNN is defined by two template matrices that
are adjusted by a properly supervised learning algorithm. After training stage for geophysical data, Bouguer anomaly maps
can be processed and analyzed sequentially. In this paper, CNN learning and processing capability have been improved, combining
Wavelet functions and backpropagation learning algorithms. The new architecture is denoted as Wavelet-Cellular Neural networks
(Wave-CNN) and it is employed to analyze Bouguer anomaly maps which are important to extract useful information in geophysics.
At first, Wave-CNN performance is tested on synthetic geophysical data, which are created by a computer environment. Then,
Bouguer anomaly maps of the Dumluca iron ore field have been analyzed and results are reported in comparison to real drilling
results. 相似文献
994.
Tsunami deposits provide a basis for reconstructing Holocene histories of great earthquakes and tsunamis on the Pacific Coast
of southwest Japan. The deposits have been found in the past 15 years at lakes, lagoons, outcrops, and archaeological excavations.
The inferred tsunami histories span 3000 years for the Nankai and Suruga Troughs and nearly 10,000 years for the Sagami Trough.
The inferred histories contain recurrence intervals of variable length. The shortest of these —100–200 years for the Nankai
Trough, 150–300 years for the Sagami Trough — resemble those known from written history of the past 1000–1500 years. Longer
intervals inferred from the tsunami deposits probably reflect variability in rupture mode, incompleteness of geologic records,
and insufficient research.
The region's tsunami history could be clarified by improving the geologic distinction between tsunami and storm, dating the
inferred tsunamis more accurately and precisely, and using the deposits to help quantify the source areas and sizes of the
parent earthquakes. 相似文献
995.
According to variations of 137Cs and clay contents, 44 flood couplets were identified in a profile of reservoir deposit with a vertical length of 28.12 m in the Yuntaishan Gully. Couplet 27 at the middle of the profile had the highest average 137Cs content of 12.65 Bq kg-1, which indicated the 1963s' deposits, then 137Cs content decreased both downward and upward in the profile. The second top and bottom couplets had average 137Cs contents of 2.15 Bq kg-1 and 0.92 Bq kg-1, respectively. By integrated analysis of reservoir construction and management history, variations of 137Cs contents over the profile, sediment yields of flood couplets and rainfall data during the period of 1958-1970, individual storms related to the flood couplets were identified. 44 floods with a total sediment yield of 2.36×104 m3 occurred and flood events in a year varied between 1 and 10 times during the period of 1960-1970. 7-10 flood events occurred during the wet period of 1961-1964 with very wet autumn, while only 1-2 events during the dry period of 1965-1969. Average annual specific sediment yield was 1.29×104 t km-2 a-1 for the Yuntaishan Gully during the period of 1960-1970, which was slightly higher than 1.11 ×104 t km-2 a-1 for the Upper Yanhe River Basin above the Ganguyi Hydrological Station and slightly lower than 1.40 ×104 t km-2 a-1 for the nearby Zhifang Gully during the same period. Annual specific sediment yields for the Yuntaishan Gully were correlated to the wet season's rainfalls well. 相似文献
996.
LI ZiYing FANG XiHeng CHEN AnPing OU GuangXi XIAO XinJian SUN Ye LIU ChiYang WANG Yi 《中国科学D辑(英文版)》2007,50(Z2):165-173
Dongsheng sandstone-type uranium deposit is located in the northern part of Ordos Basin, occurring in the transitional zones between gray-green and gray sandstones of Jurassic Zhiluo Formation. Sandstones in oxidized zone of the ore bed look gray-green, being of unique signature and different from one of ordinary inter-layered oxidation zone of sandstone-type uranium deposits. The character and origin of gray-green sandstones are systematically studied through their petrology, mineralogy and geochemistry. It is pointed out that this color of sandstones is originated from secondary oil-gas reduction processes after paleo-oxidation, being due to acicular-leaf chlorite covering surfaces of the sandstone grains. To find out the origin of gray-green sandstone and recognize paleo-oxidation zones in the ore bed are of not only theoretical significance for understanding metallogenesis of this kind of sandstone-type uranium deposit, but also very importantly practical significance for prospecting for similar kind of sandstone-type uranium deposit. 相似文献
997.
苏浙皖地区海相油气地质特征及勘探目标的选择 总被引:1,自引:0,他引:1
从晚震旦世开始至中三叠世,苏浙皖(下扬子)地区沉积了三套巨厚的海相烃源岩系,即:上震旦统一上奥陶统,石炭系-二叠系,下三叠统海相烃源岩,三套烃源岩热演化特点不同,下古生界烃源岩经历了加里东、印支-燕山期构造阶段的热演化,已达过成熟干气阶段,上古生界烃源岩基本处于生油阶段晚期;大部分三叠系烃源岩处于成熟生油阶段,少数处于未成熟阶段,区内下古生界烃源岩经历了两次成油过程,第一次发生在加里东运动前的盆地沉降阶段,第二次发生在加里东运动后晚古生代陆表海代积阶段,全区海相油气储盖条件发育,配置有利,经多年油气勘探证实,下古生界油气勘探应立足于苏北地区,上古生界油气勘探除苏北地区外,尚有皖南与浙西地区,中生界海相油气勘探应集中在区内几个发育较好的中生代盆地,如常州、句容,无为,望江盆地等。 相似文献
998.
以玲珑金矿田阜山金矿区为实测地区,研究了胶东构造岩浆岩浆活化区玲珑-焦家式金矿的矿源岩系,对2km^2内矿源岩的构造变形岩相形变进行1/2000填图。在此基础上,提出矿化趋势度(MTD)的概念并完成阜山金矿区矿化趋势度的分布图。矿化趋势度的概念及其填图研究方法对于探讨将成矿模型转化为找矿模型、逐步建立更具体量化的找矿预测实测方法有重要的参考价值和应用前景。 相似文献
999.
1000.