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1.
Evandro Luiz Klein Reginaldo Alves dos Santos Kazuo Fuzikawa Rômulo Simões Angélica 《Mineralium Deposita》2001,36(2):149-164
Fluid inclusion and structural studies were carried out at the Guarim gold deposit in the Palaeoproterozoic Tapajós province
of the Amazonian craton. Guarim is a fault-hosted gold deposit cutting basement granitoids. It consists of a quartz vein,
which is massive in its inner portions, grading laterally either to a massive or to cavity-bearing quartz vein associated
with hydrothermal breccias. The wallrock alteration comprises chlorite, carbonate, white mica and sulphide minerals, with
free gold occurring within quartz grains and spatially associated with sulphide mineral grains. Petrographic, microthermometric
and Laser Raman investigations recognised CO2-rich, mixed H2O–CO2, and H2O fluid inclusions. The coexisting CO2 and H2O–CO2 inclusions were interpreted as primary immiscible fluids that formed the gold-bearing vein. The H2O inclusions were considered a product of later infiltration of fluids unrelated to the mineralising episode. The mineralising
fluid has CO2 ranging typically from 5–10 mol%, contains traces of N2, has salinities of ∼5 wt% NaCl equiv., and densities varying between 0.85 and 0.95 g/cm3. The P–T estimations bracket gold deposition between 270–320 °C and 0.86–2.9 kb; ƒO2–ƒS2–pH estimates suggest a reduced, near-neutral character for the fluid. Variations in the physico-chemical properties, as demonstrated
by the fluid inclusion study, resulted from a combination of fluid immiscibility and pressure fluctuation. This interpretation,
combined with textural and structural evidence, suggests the emplacement of the mineralised vein in an active fault and at
a rather shallow level (4–7 km). The geological and structural setting, deposit-scale textures and structures, wallrock alteration
and physico-chemical fluid properties are compatible with those of epizonal to mesozonal orogenic lode gold deposits.
Received: 3 March 2000 / Accepted: 21 October 2000 相似文献
2.
Fluid evolution in the Rushan lode gold deposit of Jiaodong Peninsula, eastern China 总被引:2,自引:0,他引:2
Fang-Fang Hu Hong-Rui Fan Ming-Guo Zhai Cheng-Wei Jin 《Journal of Geochemical Exploration》2006,89(1-3):161
The Rushan gold deposit in the Jiaodong Peninsula is currently the largest lode gold in China. Gold occurs mainly in pyrite- and polymetallic sulfide–quartz vein/veinlet stockworks. Fluid inclusions in the deposit are divided into three main types, namely CO2–H2O, H2O–CO2 ± CH4 and aqueous ones. Microthermometric data show that the pre-gold fluids were CO2-dominant (XCO2 up to 0.53), and the total homogenization temperatures fall in the range of 298377 °C. These fluids, modified by fluid/wallrock reactions, gradually evolved into fluids with less CO2 (XCO2 = 0.010.19) in the main ore-forming stage, and the total homogenization temperatures range from 170 to 324 °C. Hydrogen and oxygen stable isotope data suggest that ore-forming fluids were mixture of magmatic and meteoritic origin. Co-occurrence of gold and sulfides implies that gold was most likely transported in the form of gold–sulfide complexes. The wide distribution of CO2 inclusions means that the pH variation during gold transportation was controlled by CO2 buffering. 相似文献
3.
Guoxiang Chi Benoît Dubé Kenneth Williamson Anthony E. Williams-Jones 《Mineralium Deposita》2006,40(6-7):726-741
The Campbell-Red Lake gold deposit in the Red Lake greenstone belt, with a total of approximately 840 t of gold (past production + reserves) and an average grade of 21 g/t Au, is one of the largest and richest Archean gold deposits in Canada. Gold mineralization is mainly associated with silicification and arsenopyrite that replace carbonate veins, breccias and wallrock selvages. The carbonate veins and breccias, which are composed of ankerite ± quartz and characterized by crustiform–cockade textures, were formed before and/or in the early stage of penetrative ductile deformation, whereas silicification, arsenopyrite replacement and gold mineralization were coeval with deformation. Microthermometry and laser Raman spectroscopy indicate that fluid inclusions in ankerite and associated quartz (Q1) and main ore-stage quartz (Q2) are predominantly carbonic, composed mainly of CO2, with minor CH4 and N2. Aqueous and aqueous–carbonic inclusions are extremely rare in both ankerite and quartz. H2O was not detected by laser Raman spectroscopic analyses of individual carbonic inclusions and by gas chromatographic analyses of bulk samples of ankerite and main ore-stage quartz (Q2). Fluid inclusions in post-mineralization quartz (Q3) are also mainly carbonic, but proportions of aqueous and aqueous–carbonic inclusions are present. Trace amounts of H2S were detected by laser Raman spectroscopy in some carbonic inclusions in Q2 and Q3, and by gas chromatographic analyses of bulk samples of ankerite and Q2. 3He/4He ratios of bulk fluid inclusions range from 0.008 to 0.016 Ra in samples of arsenopyrite and gold. Homogenization temperatures (T
h–CO2) of carbonic inclusions are highly variable (from −4.1 to +30.4°C; mostly to liquid, some to vapor), but the spreads within individual fluid inclusion assemblages (FIAs) are relatively small (within 0.5 to 10.3°C). Carbonic inclusions occur both in FIAs with narrow T
h–CO2 ranges and in those with relatively large T
h–CO2 variations. The predominance of carbonic fluid inclusions has been previously reported in a few other gold deposits, and its significance for gold metallogeny has been debated. Some authors have proposed that formation of the carbonic fluid inclusions and their predominance is due to post-trapping leakage of water from aqueous–carbonic inclusions (H2O leakage model), whereas others have proposed that they reflect preferential trapping of the CO2-dominated vapor in an immiscible aqueous–carbonic mixture (fluid unmixing model), or represent an unusually H2O-poor, CO2-dominated fluid (single carbonic fluid model). Based on the FIA analysis reported in this study, we argue that although post-trapping modifications and host mineral deformation may have altered the fluid inclusions in varying degrees, these processes were not solely responsible for the formation of the carbonic inclusions. The single carbonic fluid model best explains the extreme rarity of aqueous inclusions but lacks the support of experimental data that might indicate the viability of significant transport of silica and gold in a carbonic fluid. In contrast, the weakness of the unmixing model is that it lacks unequivocal petrographic evidence of phase separation. If the unmixing model were to be applied, the fluid prior to unmixing would have to be much more enriched in carbonic species and poorer in water than in most orogenic gold deposits in order to explain the predominance of carbonic inclusions. The H2O-poor, CO2-dominated fluid may have been the product of high-grade metamorphism or early degassing of magmatic intrusions, or could have resulted from the accumulation of vapor produced by phase separation external to the site of mineralization.Geological Survey of Canada contribution 2004383. 相似文献
4.
Fluid inclusions were studied in quartz samples from early (stage I) gold-poor quartz veins and later (stage II) gold- and
sulphide-rich quartz veins from the Wenyu, Dongchuang, Qiangma, and Guijiayu mesothermal gold deposits in the Xiaoqinling
district, China. Fluid inclusion petrography, microthermometry, and bulk gas analyses show remarkably consistent fluid composition
in all studied deposits. Primary inclusions in quartz samples are dominated by mixed CO2-H2O inclusions, which have a wide range in CO2 content and coexist with lesser primary CO2-rich and aqueous inclusions. In addition, a few secondary aqueous inclusions are found along late-healed fractures. Microthermometry
and bulk gas analyses suggest hydrothermal fluids with typically 15–30 mol% CO2 in stage I inclusions and 10–20 mol% CO2 in stage II inclusions. Estimates of fluid salinity decrease from 7.4–9.2 equivalent wt.% NaCl to 5.7–7.4 equivalent wt.%
NaCl between stage I and II. Primary aqueous inclusions in both stages show consistent salinity with, but slightly lower Th
total than, their coexistent CO2-H2O inclusions. The coexisting CO2-rich, CO2-H2O, and primary aqueous inclusions in both stage I and II quartz are interpreted to have been trapped during unmixing of a
homogeneous CO2-H2O parent fluid. The homogenisation temperatures of the primary aqueous inclusions give an estimate of trapping temperature
of the fluids. Trapping conditions are typically 300–370 °C and 2.2 kbar for stage I fluids and 250–320 °C and 1.6 kbar for
stage II fluids. The CO2-H2O stage I and II fluids are probably from a magmatic source, most likely devolatilizing Cretaceous Yanshanian granitoids.
The study demonstrates that gold is largely deposited as pressures and temperatures fall accompanying fluid immiscibility
in stage II veins.
Received: 15 May 1997 / Accepted: 10 June 1998 相似文献
5.
Auriferous quartz veins in the Hill End goldfield, NSW, Australia, comprise bedding-parallel vein sets and minor extension
and fault-controlled veins which are hosted by a multiply deformed, Late Silurian slate-metagreywacke turbidite sequence.
Fluid inclusions in quartz, either from bedding-parallel veins or from narrow, steeply N-dipping veins (‘leader’ veins) indicate
a similar range in homogenisation temperatures (Th) from 350°C to 110°C. Within this range, Th data demonstrate five groupings in the temperature intervals 350–280°C, 280–250°C, 250–190°C, 190–150°C, and 150–110°C, corresponding
to a variety of primary and secondary inclusions developed during five periods of vein growth under a generally declining
temperature regime. Inclusion fluids are characterised by a low salinity of around 0.1 to 3.6 wt% NaCl equivalent. Laser Raman
microprobe inclusion analysis indicates that gas-phase compositions relate to the paragenetic stage of the host quartz. H2O(g) and N2 dominate in the primary inclusions from barren, Stage I quartz; CH4 and CH4 + H2O(g) are important in inclusions related to the early gold forming events (equivalent to Stages II and III quartz), but inclusions
developed during the last episode of gold deposition are characterised by H2O(g), CO2-rich and liquid-CO2 bearing fluids. Precipitation of gold was aided by sulphidation reactions or phase separation in response to periods of vein
opening. Late in the paragenesis, gold deposition may have been promoted by oxidation of the ore fluid. 相似文献
6.
Non-aqueous CO2 and CO2-rich fluid inclusions are found in the vein quartz hosting mesothermal gold-sulphide mineralization at Bin Yauri, northwestern
Nigeria. Although mineralizing fluids responsible for gold mineralization are thought to be CO2-rich, the occurrence of predominantly pure to nearly pure CO2 inclusions is nevertheless unusual for a hydrothermal fluid system. Many studies of similar CO2-rich fluid inclusions, mainly in metamorphic rocks, proposed preferential loss (leakage) of H2O from H2O-CO2 inclusions after entrapment. In this study however, it is proposed that phase separation (fluid immiscibility) of low salinity
CO2-rich hydrothermal fluids during deposition of the gold mineralization led to the loss of the H2O phase and selective entrapment of the CO2. The loss of H2O to the wallrocks resulted in increasing oxidizing effects. There is evidence to suggest that the original CO2-rich fluid was intrinsically oxidized, or perhaps in equilibrium with oxidizing conditions in the source rocks. The source
of the implicated fluid is thought to be subducted metasediments, subjected to dehydration and devolatilization reactions
along a transcurrent Anka fault/shear system, which has been described as a Pan-African (450–750 Ma) crustal suture. 相似文献
7.
Evidence for fluid phase separation in high-grade ore zones at the Porgera gold deposit, Papua New Guinea 总被引:1,自引:0,他引:1
Coexisting, liquid-rich and vapor-rich primary fluid inclusions in quartz provide direct evidence for fluid phase separation
in high-grade quartz–roscoelite–gold veins and breccias from the Porgera alkalic-type gold deposit. Vapor-rich fluid inclusions
are CO2-rich, and sometimes contain liquid CO2 at room temperature. The close spatial and paragenetic relationship between these “boiling assemblage” fluid inclusions and
gold suggests that gold was precipitated by phase separation, at least locally. Additionally, the occurrence of carbonate
and sulfate minerals in high-grade veins (reflecting pH increase and oxidation of the boiled fluid) and the appearance of
hydrothermal breccias, are consistent with the process of fluid phase separation. Liquid CO2-bearing fluid inclusions are rare in near-surface epithermal deposits, and indicate that the Porgera vein system was formed
at greater depths and pressures (our estimates suggest pressures between 250 and 340 bars). It is suggested that alkalic-type
gold deposits may be distinguished from other epithermal deposit types by the more gaseous nature of the ore-forming fluids,
in addition to their association with alkalic magmas.
Received: 24 February 2000 / Accepted: 6 April 2000 相似文献
8.
雪鸡坪铜矿床产于印支晚期石英二长闪长玢岩-石英闪长玢岩-石英二长斑岩复式侵入体内,为一斑岩型铜矿床。矿床形成经历了多阶段热液成矿作用,主要有微细脉浸染状黄铁矿±黄铜矿-石英、细脉状辉钼矿±黄铁矿±黄铜矿-石英及微细脉状贫硫化物-石英-方解石等。流体包裹体岩相学、显微测温、激光拉曼及碳、氢、氧同位素综合研究表明,微细脉浸染状黄铁矿±黄铜矿-石英阶段石英中主要发育含Na Cl子矿物三相及气液两相包裹体,与含矿的石英二长斑岩石英中发育的流体包裹体特征相似,表明成矿流体主要为中高温、高盐度Na Cl-H2O体系热液,可能主要来源于印支期石英二长斑岩侵入体;辉钼矿±黄铁矿±黄铜矿-石英中主要发育含CO2三相及气液两相包裹体,成矿流体为中温、低盐度Na Cl-CO2-H2O体系热液,与前者来源明显不同;贫硫化物-石英-方解石石英中主要发育气液两相包裹体,成矿流体为中低温、低盐度Na Cl-H2O体系热液,推测其可能较多来自于大气降水。因此,雪鸡坪铜矿床为不同来源、不同地球化学性质热液叠加成矿作用的结果。 相似文献
9.
High CO2 content of fluid inclusions in gold mineralisations in the Ashanti Belt, Ghana: a new category of ore forming fluids? 总被引:4,自引:0,他引:4
Fluid inclusions were studied in samples from the Ashanti, Konongo-Southern Cross, Prestea, Abosso/Damang and Ayanfuri gold
deposits in the Ashanti Belt, Ghana. Primary fluid inclusions in quartz from mineralised veins of the Ashanti, Prestea, Konongo-Southern
Cross, and Abosso/Damang deposits contain almost exclusively volatile species. The primary setting of the gaseous (i.e. the
fluid components CO2, CH4 and N2) fluid inclusions in clusters and intragranular trails suggests that they represent the mineralising fluids. Microthermometric
and Raman spectroscopic analyses of the inclusions revealed a CO2 dominated fluid with variable contents of N2 and traces of CH4. Water content of most inclusions is below the detection limits of the respective methods used. Aqueous inclusions are rare
in all samples with the exception of those from the granite-hosted Ayanfuri mineralisation. Here inclusions associated with
the gold mineralisation contain a low salinity (<6 eq.wt.% NaCl) aqueous solution with variable quantities of CO2. Microthermometric investigations revealed densities of the gaseous inclusions of 0.65 to 1.06 g/cm3 at Ashanti, 0.85 to 0.98 g/cm3 at Prestea, up to 1.02 g/cm3 at Konongo-Southern Cross, and 0.8 to 1.0 g/cm3 at Abosso/Damang. The fluid inclusion data are used to outline the PT ranges of gold mineralisation of the respective gold deposits. The high density gaseous inclusions found in the auriferous
quartz at Ashanti and Prestea imply rather high pressure trapping conditions of up to 5.4 kbar. In contrast, mineralisation
at Ayanfuri and Abosso/Damang is inferred to have occurred at lower pressures of only up to 2.2 kbar. Mesothermal gold mineralisation
is generally regarded to have formed from fluids characterized by H2O > CO2 and low salinity ( ± 6 eq.wt.%NaCl). However, fluid inclusions in quartz from the gold mineralisations in the Ashanti belt
point to distinctly different fluid compositions. Specifically, the predominance of CO2 and CO2 >> H2O have to be emphasized. Fluid systems with this unique bulk composition were apparently active over more than 200␣km along
strike of the Ashanti belt. Fluids rich in CO2 may present a hitherto unrecognised new category of ore-forming fluids.
Received: 30 May 1996 / Accepted: 8 October 1996 相似文献
10.
Basem A. Zoheir 《Mineralium Deposita》2008,43(1):79-95
The Betam gold deposit, located in the southern Eastern Desert of Egypt, is related to a series of milky quartz veins along
a NNW-trending shear zone, cutting through pelitic metasedimentary rocks and small masses of pink granite. This shear zone,
along with a system of discrete shear and fault zones, was developed late in the deformation history of the area. Although
slightly sheared and boudinaged within the shear zone, the auriferous quartz veins are characterised by irregular walls with
a steeply plunging ridge-in-groove lineation. Shear geometry of rootless intra-folial folds and asymmetrical strain shadows
around the quartz lenses suggests that vein emplacement took place under a brittle–ductile shear regime, clearly post-dating
the amphibolite-facies regional metamorphism. Hydrothermal alteration is pervasive in the wallrock metapelites and granite
including sericitisation, silicification, sulphidisation and minor carbonatisation. Ore mineralogy includes pyrite, arsenopyrite
and subordinate galena, chalcopyrite, pyrrhotite and gold. Gold occurs in the quartz veins and adjacent wallrocks as inclusions
in pyrite and arsenopyrite, blebs and globules associated with galena, fracture fillings in deformed arsenopyrite or as thin,
wire-like rims within or around rhythmic goethite. Presence of refractory gold in arsenopyrite and pyrite is inferred from
microprobe analyses. Clustered and intra-granular trail-bound aqueous–carbonic (LCO2 + Laq ± VCO2) inclusions are common in cores of the less deformed quartz crystals, whereas carbonic (LCO2 ± VCO2) and aqueous H2O–NaCl (L + V) inclusions occur along inter-granular and trans-granular trails. Clathrate melting temperatures indicate low
salinities of the fluid (3–8 wt.% NaCl eq.). Homogenisation temperatures of the aqueous–carbonic inclusions range between
297 and 323°C, slightly higher than those of the intra-granular and inter-granular aqueous inclusions (263–304°C), which are
likely formed during grain boundary migration. Homogenisation temperatures of the trans-granular H2O–NaCl inclusions are much lower (130–221°C), implying different fluids late in the shear zone formation. Fluid densities
calculated from aqueous–carbonic inclusions along a single trail are between 0.88 and 0.98 g/cm3, and the resulting isochores suggest trapping pressures of 2–2.6 kbar. Based on the arsenopyrite–pyrite–pyrrhotite cotectic,
arsenopyrite (30.4–30.7 wt.% As) associated with gold inclusions indicates a temperature range of 325–344°C. This ore paragenesis
constrains f
S2 to the range of 10−10 to 10−8.5 bar. Under such conditions, gold was likely transported mainly as bisulphide complexes by low salinity aqueous–carbonic fluids
and precipitated because of variations in pH and f
O2 through pressure fluctuation and CO2 effervescence as the ore fluids infiltrated the shear zone, along with precipitation of carbonate and sericite. Wallrock
sulphidation also likely contributed to destabilising the gold–bisulphide complexes and precipitating gold in the hydrothermal
alteration zone adjacent to the mineralised quartz veins. 相似文献