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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
2.
At the Sandpiper gold deposit in the Tanami region of northern Australia sericite is intimately intergrown with arsenopyrite in gold-bearing quartz veins and breccias, suggesting sericite crystallisation synchronous with gold-bearing fluid flow. This ore-stage sericite yields a 40Ar/39Ar plateau age of 1785 ± 32 Ma (2σ including both analytical and systematic uncertainties). Recalculation using revised and more precise values for the 40K decay constants and the age of the Fish Canyon Sanidine standard shifts the age to 1794 ±12 Ma (2σ including all known uncertainties). Given the possibility of post-mineralisation isotopic resetting this age can be conservatively interpreted as a minimum constraint on the timing of gold deposition although, given local geological relationships and estimates for the argon retentivity of white mica, we consider complete isotopic resetting to be unlikely. The preferred interpretation is, therefore, that the sericite 40Ar/39Ar age indicates the timing of gold mineralisation. Thesericite age accords with a limited dataset of 207Pb/206Pb xenotime ages of ca 1800 Ma from other gold deposits in the Tanami region, interpreted as mineralisation ages. The agreement between independently derived ages from several gold deposits lends support for a widespread gold-mineralising event at ca 1800 Ma in the Tanami region. 相似文献
3.
Provenance,tectonic setting and source of Archean metasedimentary rocks of the Browns Range Metamorphics,Tanami Region,Western Australia 总被引：1，自引：0，他引：1
T. Nazari-Dehkordi C. Spandler N. H. S. Oliver J. Chapman R. Wilson 《Australian Journal of Earth Sciences》2017,64(6):723-741
This study combines U–Pb age and Lu–Hf isotope data for magmatic and detrital zircons, with whole-rock geochemistry of the Browns Range Metamorphics (BRM), Western Australia. The BRM are medium- to coarse-grained metasandstones that consist of angular to sub-rounded detrital quartz and feldspars with minor granitic lithic fragments. The sequence has undergone partial to extensive quartz–muscovite alteration and rare-earth-element mineralisation and has been intruded by mafic/ultramafic, syenitic and pegmatitic intrusive rock units. Uranium–Pb and Lu–Hf isotopic data on detrital zircons from the metasandstones and intruding granitic rocks yield a well-defined age of ca 3.2 to ca 3.0 Ga for all samples, with relatively radiogenic ?Hf values (?Hf = –1.7 to 5.1) indicating derivation from Mesoarchean granite basement of juvenile origin. This is consistent with geochemical and petrological data that support deposition from a granitic source in a continental rift basin setting. The timing of sediment deposition is constrained between the ca 3.0 Ga age of the source rocks and ca 2.5 Ga age of the granitic intrusive bodies that cross-cut the metasedimentary rocks. The ca 2.5 Ga zircons from the intrusive rocks have ?Hf model ages of ca 3.4 to ca 3.1 Ga, which is consistent with formation via partial melting of the BRM, or the Mesoarchean granite basement. Zircons of the Gardiner Sandstone that unconformably overlies the BRM return detrital ages of ca 2.6 to ca 1.8 Ga with no trace of ca 3.1 Ga zircons, which discounts a significant contribution from the underlying BRM. The Mesoarchean age and isotopic signatures of the BRM zircons are shared by some zircon records from the Pine Creek Orogen, and the Pilbara, Yilgarn and Gawler cratons. Collectively, these records indicate that juvenile Mesoarchean crust is a more significant component of Australian cratons than is currently recognised. This work also further demonstrates that detrital minerals in Paleoproterozoic/Archean sedimentary rocks are archives to study the early crustal record of Earth. 相似文献
4.
Geological and structural controls on gold mineralization in the Tanami District, Northern Territory
Gold mineralization in the Tanami district is hosted within moderately northwest dipping turbiditic sedimentary and basaltic
volcanic rocks of the Paleoproterozoic Mt. Charles Formation. The gold occurs within a complex sinistral wrench-fault array
and associated veins and alteration haloes. The main mineralized faults have a northerly trend and dip steeply east. Subsidiary
structures trend at 030° and 070° and dip towards the southeast. Paleostress calculations based on fault striation populations
and geometry (strike and dip) of faults indicate that at the time of the mineralizing event, σ
1 was sub-horizontal and SE–NW directed with σ
2 subvertical. Structural studies indicate that the mineralization occurred after the regional folding event and synchronous
with the emplacement of felsic dykes into the mine sequence. Gold veins in the Tanami district are interpreted to be part
of an outer thermal aureole gold system that formed during the emplacement of granitoids in the nearby ∼1,815 to ∼1,799 Ma
Frankenia and/or Coomarie domes. Economic gold mineralization occurred late in the paragenetic history of the district. Gold
is hosted by quartz-carbonate veins within shear zones, and also in the surrounding sericite- quartz- pyrite ± carbonate-altered
wallrocks. Gold-mineralized veins precipitated at depths of 3 to 6 km from high temperature (∼300°C), low salinity (∼5 wt%
NaCl equivalent) fluids with low CO2 contents. Barren quartz, dolomite and calcite veins that occur in pre- and post-mineralization thrust faults formed from
high salinity (∼20 wt% NaCl equivalent), low temperature (∼120–150°C) basinal brines. Pyrite in the gold mineralized veins
and alteration halos has lower δ
34S values (6.8 to 12.5‰) than local diagenetic pyrite (17.8 to 19.2‰) or pyrite in pre-mineralization thrust faults (31.7 to
37.1‰). The mineralizing fluids are inferred to have contained a well-homogenized mixture of magmatic and sedimentary-derived
sulfur.
Editorial handling: D. Huston 相似文献
5.
Poorly exposed Paleoproterozoic turbiditic to shallow marine sedimentary rocks of the Tanami Basin, NT, Australia are largely
the erosional products of either the ∼1.87–1.85 Hooper Orogeny and/or magmatism associated with the ∼1.87 Ga Nimbuwah Event.
Dating of detrital zircon from six of the principal sedimentary units shows that deposition spanned at least the period ∼1.84–1.77 Ga.
Collectively, the detrital zircon ages reveal a progression in provenance that is a record of the development of the orogen.
The basal Dead Bullock Formation contains only zircon derived from Archean basement and no contemporaneous products of orogeny.
Its deposition age is inferred to be ∼1.87–1.84 Ga. Orogenic ∼1.86 Ga zircon appears in the overlying Killi Killi Formation,
deposited between ∼1.84–1.82 Ga and persists, probably due to recycling in all overlying units except one, the Mount Charles
Formation. The accepted stratigraphic position of this unit might be incorrect.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
6.
Nicholas C. Williams 《Mineralium Deposita》2007,42(1-2):65-87
The Callie deposit is the largest (6.0 Moz Au) of several gold deposits in the Dead Bullock Soak goldfield of the Northern
Territory’s Tanami Region, 550 km northwest of Alice Springs. The Callie ore lies within corridors, up to 180 m wide, of sheeted
en echelon quartz veins where they intersect the 500-m-wide hinge of an ESE-plunging F1 anticlinorium. The host rocks are the Blake beds, of the Paleoproterozoic Dead Bullock Formation, which consist of a > 350-m-thick
sequence of lower greenschist facies graphitic turbidites and mudstones overlying in excess of 100 m of thickly bedded siltstones
and fine sandstones. The rocks are Fe-rich and dominated by assemblages of chlorite and biotite, both of which are of hydrothermal
and metamorphic origin. A fundamental characteristic of the hydrothermal alteration is the removal of graphite, a process
which is associated with bleaching and the development of bedding-parallel bands of coarse biotite augen. Gold is found only
in quartz veins and only where they cut decarbonized chloritic rock with abundant biotite augen and no sulfide minerals. Auriferous
quartz veins differ from barren quartz veins by the presence of ilmenite, apatite, xenotime, and gold and the absence of sulfide
minerals. The assemblage of gold–ilmenite–apatite–xenotime indicates a linked genesis and mobility of Ti, P, and Y in the
mineralizing fluids. Geochemical analysis of samples throughout the deposit shows that gold only occurs in sedimentary rocks
with high FeO/(FeO+Fe2O3) and low C/(C+CO2) ratios (> 0.8 and < 0.2, respectively). This association can be explained by reactions that convert C from reduced graphitic
host rocks into CO2 and reduce ferric iron in the host rocks to ferrous iron in biotite and chlorite. These reactions would increase the CO2 content of the fluid, facilitating the transport of Ti, P, and Y from the host rocks into the veins. Both CO2 and CH4 produced by reaction of H2O with graphite, effervesced under the lower confining pressures in the veins. This would have partitioned H2S into the vapor phase, destabilizing Au–bisulfide complexes; the loss of CO2 and H2S from the aqueous phase caused precipitation of gold, ilmenite, apatite, and xenotime. It is proposed that this process was
the main control on gold precipitation. Oxidization of iron in the very reduced wall rocks, resulting in reduction of the
fluid, provided a second mechanism of gold precipitation in previously decarbonized rocks, contributing to the high grades
in some samples. Although sulfide minerals, especially arsenopyrite, did form during the hydrothermal event, host rock sulfidation
reactions did not play a role in gold precipitation because gold is absent near rocks or veins containing sulfide minerals.
Sulfide minerals likely formed by different mechanisms from those associated with gold deposition. Both the fold architecture
and subsequent spatially coincident sinistral semibrittle shearing ensured that the ore fluids were strongly focused into
the hinges of the anticlines. Within the anticlines, a reactive cap of fine-grained, graphitic, reduced Fe-rich turbidites
above more permeable siltstones and fine sandstones impeded fluid flow ensuring efficient removal of graphite, and the associated
effervescence of CO2 from the fluid caused the precipitation of gold. Exploration for similar deposits should focus on the intersection of east–west
shear zones with folds and Fe-rich graphitic host rocks. 相似文献
7.
The Tanami Region, a poorly exposed, mostly Paleoproterozoic province within the North Australian Craton, hosts a number of
significant gold deposits in diverse settings. Rare exposures of 2,520–2,500 Ma amphibolite facies Archean gneiss and metasedimentary
rocks form basement to the thick overlying metasedimentary succession of the 1,880–1,830 Ma Tanami Group. The basal unit of
the Tanami Group is the Dead Bullock Formation, a fining-upward deep-water succession dominated by siltstone, carbonaceous
siltstone, iron-rich siltstone and mafic sills. Carbonaceous- and iron-rich lithologies in the upper Dead Bullock Formation
represent important hosts for gold mineralization. The conformably overlying Killi Killi Formation represents turbiditic sedimentary
rocks that are correlated with the widespread Lander Rock beds of the Arunta Region. Sedimentation of the Tanami Group was
terminated by regional deformation and greenschist to amphibolite facies metamorphism during the Tanami Event (D1/M1), at around 1,830 Ma. The Tanami Group is unconformably overlain by rhyolite, siliciclastic sedimentary rocks, and felsic
ignimbrite of the Ware Group that were deposited at about 1,825–1,810 Ma. Subsequent ESE–WNW to SE–NW directed shortening
(D2), followed by NE–SW to E–W directed shortening (D3), has resulted in open NE F2- and NW F3-trending folds in both the Tanami and Ware Groups. Voluminous granitoids, dominated by I-type, biotite granodiorite, and
monzogranite were intruded in the interval 1,825–1,790 Ma and have been subdivided using geochemical criteria into the Birthday,
Frederick, and Grimwade Suites. Basalt and immature sedimentary rocks of the Mount Charles Formation are restricted in extent
to the Tanami mine corridor, and are interpreted to reflect a continental rift succession that was deposited around 1,800 Ma,
with an early Archean sedimentary provenance. Steep S to SE dipping F4-fold structures of Tanami and Ware Group metasedimentary rocks, many spatially associated with 1,825–1,790 Ma granitoid intrusions,
indicate a period of SSE-directed regional shortening (D4) syn-to-post the regional granitoid intrusive phase. A network of N to NW striking faults, several of which are interpreted
as oblique thrusts with a component of left lateral movement, indicates a period of D5 convergence during WSW–ENE to E–W directed shortening. The Tanami mine corridor fault system comprises a network of N, NE
to ENE striking D5 faults that merge with N to NW striking faults and probably accommodated movement between granite core domains. D5 faulting is associated with the main phase of gold mineralization in suitable structural–lithological traps. The Paleoproterozoic
basement of the Tanami Region is unconformably overlain by quartz sandstone, lithic arenite, and conglomerate of the Pargee
Sandstone. Pargee Sandstone may represent syn-tectonic sedimentation related to the 1,730 Ma Strangways Orogeny, and is unconformably
overlain by the late Paleoproterozoic platform cover succession of the Birrindudu Group. The Paleoproterozoic basement and
cover sequences have subsequently undergone several episodes of faulting, collectively termed D6+. The Paleoproterozoic evolution of the Tanami Region is interpreted to have occurred in an intracratonic setting, but was
fundamentally influenced by tectonic events in the adjacent Halls Creek Orogen (1,835–1,805 Ma Halls Creek Orogeny) and Arunta
Region (1,815–1,800 Ma Stafford Event). The boundaries between the Tanami Region and Kimberley Region to the northwest and
the Arunta Region to the southeast are transitional, and are largely defined by the presence or absence of identifiable Dead
Bullock Formation. 相似文献
8.
The ore deposits of The Granites goldfield are shear-hosted within Palaeoproterozoic amphibolite facies metasedimentary rocks
in the Tanami Region, Northern Territory, Australia. The ore bodies are located within a 5- to 35-m thick sequence of steeply
dipping unit of metamorphosed iron-rich metasedimentary rocks. Deformation at The Granites was complex and is characterized
by five successive deformation phases (D1–5). Shear veins (central and oblique) are the dominant type of vein geometry, with minor development of extensional veins and
reverse-fault related veins. Four generations of syn-tectonic veins, corresponding to D1, D3, D4, and D5, have been recognized and are comprised of quartz, quartz-carbonate, calc-silicate, and calcite. In addition, two generations
of disseminated sulfide–arsenide mineralization, dominated by pyrrhotite, arsenopyrite, and loellingite, with minor pyrite,
chalcopyrite and rare marcasite, formed syn-D1 and syn- to post-D3. Textural and structural evidence indicates deposition of gold was contemporaneous with the syn-D1 veins and sulfide–arsenide mineralization. Four hydrothermal phases are proposed for the formation of the veins and disseminated
sulfide–arsenide assemblages. The first phase (D1) was responsible for transport and deposition of the majority of the gold. Minor remobilization and deposition of gold occurred
during the D3 and D4 phases. Little is known about the nature of the D1 ore fluid, although a relatively low sulfur content is indicated by the assemblage pyrrhotite–arsenopyrite–loellingite+rare
pyrite. The growth of amphibolite facies metamorphic minerals andalusite and almandine garnet during D1 indicates a high temperature for the fluid. The D3 hydrothermal phase coincided with peak metamorphism. D4 fluids were hypersaline, high temperature, CO2-poor, and H2S-poor.
Editorial handling: L. Meinert 相似文献
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