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971.
Timothy Baker Roger Mustard Bin Fu Patrick J. Williams Guoyi Dong Louise Fisher Geordie Mark Chris G. Ryan 《Mineralium Deposita》2008,43(6):599-608
Proterozoic rocks of the Cloncurry district in NW Queensland, Australia, are host to giant (tens to hundreds of square kilometers)
hydrothermal systems that include (1) barren regional sodic–calcic alteration, (2) granite-hosted hydrothermal complexes with
magmatic–hydrothermal transition features, and (3) iron oxide–copper–gold (IOCG) deposits. Fluid inclusion microthermometry
and proton-induced X-ray emission (PIXE) show that IOCG deposits and the granite-hosted hydrothermal complexes contain abundant
high temperature, ultrasaline, complex multisolid (type 1) inclusions that are less common in the regional sodic–calcic alteration.
The latter is characterized by lower salinity three-phase halite-bearing (type 2) and two-phase (type 3) aqueous inclusions.
Copper contents of the type 1 inclusions (>300 ppm) is higher than in type 2 and 3 inclusions (<300 ppm), and the highest
copper concentrations (>1,000 ppm) are found both in the granite-hosted systems and in inclusions with Br/Cl ratios that are
consistent with a magmatic source. The Br/Cl ratios of the inclusions with lower Cu contents are consistent with an evaporite-related
origin. Wide ranges in salinity and homogenization temperatures for fluid inclusions in IOCG deposits and evidence for multiple
fluid sources, as suggested by halogen ratios, indicate fluid mixing as an important process in IOCG genesis. The data support
both leaching of Cu by voluminous nonmagmatic fluids from crustal rocks, as well as the direct exsolution of Cu-rich fluids
from magmas. However, larger IOCG deposits may form from magmatic-derived fluids based on their higher Cu content. 相似文献
972.
The Hyde-Macraes Shear Zone (HMSZ) is a regionally continuous, low-angle, NE dipping (~15°) late-metamorphic thrust zone in
the Mesozoic Otago Schist. The shear zone, which is host to large volumes of mineralised schist, consists of foliated fissile
schist with some massive schist pods. Two sets of quartz veins are found within the HMSZ: thrust-related, shallowly dipping
veins that were emplaced parallel or sub-parallel to the shears and swarms of steeply dipping extensional veins, which cut
across the metamorphic foliation. The latter are restricted to the massive schist pods. Mutual cross-cutting relationships
occur between steep extensional veins and shallow-dipping veins, suggesting that they formed contemporaneously. The co-existence
of these two vein types locally implies local rotation of the principal stress axes to produce extensional veins within a
regional thrust setting. The steep extensional veins are spatially related to lateral and oblique ramps within the HMSZ. Three-dimensional
mechanical models show that these lateral or oblique ramps can produce favourable conditions for extensional vein formation
when combined with a high fluid pressure and oblique convergence. Mechanical requirements include a reduced differential stress,
a positive volumetric strain and an increase in the horizontal shear stress. Our models show that under certain conditions,
it is possible for extension-related structures to form during shortening because of local changes in the stress state without
the need for a regional scale switch in the imposed stress field. The convergence direction across the HMSZ during formation
of the steep extensional veins was ~WNW. 相似文献
973.
Farahnaz Daliran 《Mineralium Deposita》2008,43(4):383-404
The disseminated gold deposit of Agdarreh (24.5 t at 3.7 g/t Au) is hosted in hydrothermally leached Miocene reefal limestone
in the Takab geothermal field, which is part of the Cenozoic Urumieh–Dokhtar volcanic arc of NW Iran. Alteration and mineralisation
are largely bedding controlled blanket-like and include: (1) pre-ore decalcification; (2) first-stage silicification associated
with pyrite (early pyrite with 3–4 wt% As, late pyrite with <1–3 wt% As) and sphalerite; (3) second-stage silicification with
precipitation of galena, Pb–Sb–As sulphides, sulphosalts, tellurides and native bismuth; (4) late-stage cinnabar and barite
in vugs; (5) oxide ore stage and carbonate alteration (complex Mn–Fe-rich oxyhydroxides, arsenates, sulphates, APS minerals
and rutile in residual leached rock and infill of karstic cavities). Gold occurs invisibly in the jasperoids and is enriched
in the Mn–Fe oxyhydroxide surface cap of the jasperoids. Gold mineralisation is associated with the hydrothermal metal suite
of As, Sb, Hg, Te, Se, Tl, Ba, Zn, Ag, Cd, Bi and Pb, and is characterised by very low Cu contents. Arsenian pyrite probably
carried most of the primary (invisible) gold. Native gold occurs in association with the late-stage cinnabar and the oxide
ore.
The Agdarreh deposit shows many similarities with Carlin-type ore and is interpreted to have resulted from near-surface hydrothermal
activity related to the Cenozoic arc volcanism that developed within the extensional Takab graben. The extensive oxidation
at Agdarreh may be partly due to the waning stages of hydrothermal activity. Active H2S-bearing thermal springs are locally depositing extremely high contents of Au and Ag, and travertine is present over large
areas, suggesting that ore-forming hydrothermal activity occurred periodically from the Miocene to Recent in the Takab geothermal
field.
The present paper deals with the geological framework, host rocks, characteristic features of hydrothermal alteration and
mineralisation, and genesis of the Agdarreh deposit. The results of fluid inclusion and stable isotope studies are in progress
and will be given in a forthcoming paper. 相似文献
974.
Colombo Celso Gaeta Tassinari Fabio Diaz Pinzon Juaquin Buena Ventura 《Ore Geology Reviews》2008,33(3-4):505-518
Epigenetic gold mineralization occurs in the Marmato mining district, within the Calima Terrain of the Setentrional Andes, Colombia. Regional rocks associated with this mineralization include: graphite- and chlorite-schists of the Arquia Complex; metamorphosed during the Cretaceous, Miocene sandstones, shales and conglomerates of the Amagá Formation; as well as pyroclastic rocks (clasts of basalt, andesites and mafic lavas) and subvolcanic andesitic/dacitic bodies of the Combia Formation (9 to 6 Ma). The subvolcanic Marmato stock hosts mesothermal and epithermal low-sulfidation Au–Ag ores in the form of distensional veins, stockwork, and quartz veinlets within brecciated zones. Ore minerals are pyrite, sphalerite and galena with subordinate chalcopyrite, arsenopyrite, pyrrhotite, argentite and native gold/electrum.Sericitized plagioclase from a porphyry dacite yielded a K–Ar age of 5.6 ± 0.6 Ma, interpreted as the age of ore deposition. This is in close agreement with the age of reactivation of the Cauca–Romeral Fault System (5.6 ± 0.4 Ma), which bounds the Calima Terrain. A porphyry andesite–dacite (6.7 ± 0.1 Ma), hosting the Au–Ag veins, shows a measured 87Sr/86Sr between 0.70440 and 0.70460, εNd between + 2.2 and + 3.2 and 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 18.964 to 19.028; 15.561 to 15.570; and 38.640 to 38.745, respectively. The 87Sr/86Sr and εNd values of rocks from the Arquia Group range from 0.70431 to 0.73511 and − 12.91 to + 10.0, respectively, whereas the corresponding Pb isotopic ratios (206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb) range from 18.948 to 19.652; 15.564 to 15.702; and 38.640 to 38.885, respectively. 87Sr/86Sr and εNd values obtained on sulfides from the gold quartz veins, which occur at shallow and intermediate levels, range from 0.70500 to 0.71210 and from − 1.11 to + 2.40. In the deepest veins, εNd values lie between + 1.25 and + 3.28 and the 87Sr/86Sr of calcite and pyrite fall between 0.70444 and 0.70930. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of all mineralization are in the ranges 18.970 to 19.258; 15.605 to 15.726 and 38.813 to 39.208, respectively. Carbonates have an average 87Sr/86Sr ratio of 0.70445, which is within the range of values measured in the host dacite. The Sr isotopic data indicate that carbonic fluids have a restricted hydrothermal circulation within the host igneous body, while the Sr, Pb and Nd isotopic compositions of the sulfides suggest that the fluids not only circulated within the Marmato stock, but also throughout the Arquia Complex, inferring that these rocks offer a potential target for mineral exploration. Based on geological and geochronological evidence, the epizonal Marmato gold ores formed during the Miocene to Pliocene, as a result of cooling of the Marmato stock and reactivation along a crustal-scale fault zone related to thermal processes in an accretionary oceanic–continental plate orogen. 相似文献
975.
Mercury contamination of active channel sediment and floodplain deposits from historic gold mining at Gold Hill,North Carolina,USA 总被引:2,自引:1,他引:1
A reconnaissance investigation of mercury contamination associated with historic gold mining in North Carolina, USA, revealed
high concentrations of mercury in channel and floodplain sediments downstream from the Gold Hill mining district. The most
intense period of mining activities in this region occurred in the 1840s and 1850s when mercury amalgamation was used to recover
fine gold particles from milled ore. This paper evaluates mercury concentrations measured in active channel sediments and
two cores recovered from historic floodplain deposits of the lower portion of Dutch Buffalo Creek. Mercury concentrations
in these cores range from 0.01 to 2.2 mg/kg, with maximum concentrations more than 35 times background levels. A later peak
in copper concentrations is associated with the operation of a large copper mine between 1899 and 1906. Following the most
intense periods of mining, both mercury and copper concentrations decrease upcore to constant levels of about twice pre-mining
background concentrations. Results suggest that vertical trends in mercury and other trace metals provide a useful tool for
interpreting rates of historic floodplain sedimentation in the Piedmont of North Carolina. 相似文献
976.
The Pala region, in southwestern Chad, belongs to the northern part of the Central African Pan-African Fold Belt. It is made up of greenschist-facies schists and is characterized by bimodal, mainly mafic, magmatism. This schist unit named Goueigoudoum Series is intruded by pre- to post-tectonic plutonic rocks dated between 737 and 570 Ma and dykes of quartz. Gold is mined artisanally from alluvial deposits and primary chalcopyrite–pyrite-bearing quartz veins, brecciated and silicified zones and shear zones. The majority of the mineralized shear zones and some quartz veins generally trend N–S to NNE–SSW or NW–SE and are interpreted as extensional shear fractures related to regional NE–SW-trending sinistral strike–slip shear zones. The geological context of the Pala region clearly indicates hydrothermal fluids formed along active continental margins during collisional orogenesis, and subsequent associated fluid migration typically occurred during strike–slip events. Although the origin of fluids may be varied (magmatic, metamorphic or meteoric fluids, Proterozoic seawater, or sedimentary basin formation waters), the distribution of the mineralizations along the granitoid intrusions suggests that magmatism played a major role in the dynamics of the mineralizing fluids. 相似文献
977.
气候变化将使水利工程的服役环境发生较大改变,水工混凝土作为水利工程建设最主要的建筑材料之一,其对极端气候变化较为敏感与脆弱。本文以水库大坝、大型调水工程等水利工程为对象,系统总结了部分已观测到的低温冻害、寒潮和干旱等气候条件对水利工程影响的事实。结合未来气候变化趋势及其可能的影响,从改善水工材料性能的工程措施角度,分析了在水利工程设计、施工、运行阶段可采取的应对措施,并从规划修订、预案制订、监测预报等非工程措施角度,分析了在防洪安全、水资源安全等领域可采取的减缓适应对策,以提高水工程应对气候变化的能力。 相似文献
978.
979.
《Marine pollution bulletin》2014,78(1-2):428-433
In November 2011 gold was found at Mount Botak, Buru Island, Mollucas Province, Indonesia. Since 2012 mercury has been used to extract the gold requiring large volumes of water and resulting in deposition of mercury into Wamsait River and Kayeli Bay. Total mercury in waste ponds was over 680 mg/kg. In sediments at the mouth of the local river and a small feeder creek >3.00 mg/kg and >7.66 mg/kg respectively. River and bay sediments were proportionately higher in available mercury than elemental mercury and more strongly bound mercuric sulfide compared to that in trommel waste. This preliminary investigation raises concerns about the long term distribution and speciation of mercury. The floodplain is an important agricultural resource, and Mollucas Province is recognised nationally as the centre for Indonesian fish stocks. Challenges for management include communicating the potential future risks to the community and leaders and identifying mechanisms to reduce mercury waste. 相似文献
980.
锡林郭勒金成矿带颇具找矿潜力,文章总结了成矿带的地球物理、地球化学特征,采用数理统计分析方法,确定了矿床元素轴向分带序列为:As-Sb-Hg-Bi-Li-Sr-Ba-Ag-Pb-Au-Cu-Zn-Sn-V-Co-Cr-Ni-Ti-Mo-W,前缘晕元素为As,Sb,Hg,Bi,主成矿元素为Au,Cu,Zn,尾晕元素为Ti,Mo,W.据轴向分带特征,确定金矿体剥蚀程度的判别指标为As×Sb×Bi/Ti×Mo×W.根据研究成果部署的深部钻探工程取得了较好的找矿效果. 相似文献