scholarly journals A test of the viability of fluid–wall rock interaction mechanisms for changes in opaque phase assemblage in metasedimentary rocks in the Kambalda-St. Ives goldfield, Western Australia

2009 ◽  
Vol 45 (2) ◽  
pp. 207-213 ◽  
Author(s):  
Katy A. Evans
Keyword(s):  
Western Australia ◽  
Wall Rock ◽  
Phase Assemblage ◽  
Rock Interaction ◽  
Interaction Mechanisms ◽  
Metasedimentary Rocks

sPhysicochemical conditions of fluid–wall rock interaction at amphibolite-facies conditions in two Archean hydrothermal gold deposits in the Mt. York District, Pilbara Craton, Western Australia

1995 ◽  
Vol 32 (7) ◽  
pp. 993-1016 ◽  
Author(s):  
P. Neumayr ◽  
J.R. Ridley ◽  
D.I. Groves
Keyword(s):  
Western Australia ◽  
Gold Mineralization ◽  
Wall Rock ◽  
Gold Deposits ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Rock Interaction ◽  
Wall Rock Alteration ◽  
Geochemical Analyses ◽  
Pilbara Craton

Synamphibolite facies Archean gold mineralization in the Mt. York District, Pilbara Craton, Western Australia, is hosted in metamorphosed banded iron formation (Main Hill–Breccia Hill prospect), amphibolites, and ultramafic schists (Zakanaka prospect). Mineralization at Main Hill occurs in quartz breccias with sulfide matrices and in altered wall rock adjacent to quartz–biotite–amphibole ± clinopyroxene veins. Alteration associated with quartz veins is zoned, with biotite—pyrrhotite vein selvedges and a distal calcic-amphibole, arsenopyrite–lôllingite zone. Hydrothermal biotite and actinolite have highest Mg/(Mg + Fe) ratios where associated with abundant sulfarsenides in the distal alteratin zone. Whole-rock geochemical analyses and calculated metasomatic reactions indicate the addition of K, Al, S, As, Au, Ag, and Ni during hydrothermal alteration. Mineralization at Zakanaka is characterized by a broad wall rock alteration halo of biotite–amphibole, and zoned quartz–calc silicate veins proximal to ore. Wall rock adjacent to the veins contains pyrrhotite, pyrite, and gold. The alteration is explained by K-metasomatism distal to mineralization and K and Ca metasomatism proximal to mineralization. Balanced metasomatic reactions and mass-balance calculations indicate addition of K and depletion of Na, Ca, Mg, and Fe in distal alteration zones and addition of K, Ca, Mg, Fe, and Ti in proximal zones. Gold precipitation at both prospects occurred through loss of S, and possibly As, from the ore fluid during sulfidation reactions with Fe-rich amphiboles and biotites to form Mg-enriched equivalents and sulfarsenides. Changes in the oxidation state of the ore fluid may have enhanced gold precipitation, though pH changes are unlikely to have been important. The controls on mineralization are thus similar to those at many lower temperature, mesothermal deposits. The lack of consistently increasing Mg ratios of calc-silicate phases with increasing intensity of alteration and sulfidation at Main Hill may be the result of coupled substitutions in amphiboles and biotites during infiltration of a fluid with high-S, but low-As, activities.

scholarly journals Interpretation of Gas/Water Relative Permeability of Coal Using the Hybrid Bayesian-Assisted History Matching: New Insights

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 626
Author(s):  
Jiyuan Zhang ◽  
Bin Zhang ◽  
Shiqian Xu ◽  
Qihong Feng ◽  
Xianmin Zhang ◽  
...  
Keyword(s):  
Relative Permeability ◽  
Coalbed Methane ◽  
History Matching ◽  
Water Saturation ◽  
Unsteady State ◽  
Core Flooding ◽  
Rock Interaction ◽  
Interaction Mechanisms ◽  
True Value ◽  
Assisted History Matching

The relative permeability of coal to gas and water exerts a profound influence on fluid transport in coal seams in both primary and enhanced coalbed methane (ECBM) recovery processes where multiphase flow occurs. Unsteady-state core-flooding tests interpreted by the Johnson–Bossler–Naumann (JBN) method are commonly used to obtain the relative permeability of coal. However, the JBN method fails to capture multiple gas–water–coal interaction mechanisms, which inevitably results in inaccurate estimations of relative permeability. This paper proposes an improved assisted history matching framework using the Bayesian adaptive direct search (BADS) algorithm to interpret the relative permeability of coal from unsteady-state flooding test data. The validation results show that the BADS algorithm is significantly faster than previous algorithms in terms of convergence speed. The proposed method can accurately reproduce the true relative permeability curves without a presumption of the endpoint saturations given a small end-effect number of <0.56. As a comparison, the routine JBN method produces abnormal interpretation results (with the estimated connate water saturation ≈33% higher than and the endpoint water/gas relative permeability only ≈0.02 of the true value) under comparable conditions. The proposed framework is a promising computationally effective alternative to the JBN method to accurately derive relative permeability relations for gas–water–coal systems with multiple fluid–rock interaction mechanisms.

Comment and Reply on "Nd isotopic gradients in upper crustal magma chambers: Evidence for in situ magma-wall-rock interaction"

Geology ◽  
1991 ◽  
Vol 19 (2) ◽  
pp. 185
Author(s):  
Benjamin C. Schuraytz ◽  
Thomas A. Vogel ◽  
Leland W. Younker ◽  
G. Lang Farmer ◽  
Kathryn J. Tegtmeyer
Keyword(s):  
Wall Rock ◽  
Magma Chambers ◽  
Rock Interaction ◽  
Crustal Magma

Oxygen, hydrogen, and strontium isotope constraints on the origin of granites

1988 ◽  
Vol 79 (2-3) ◽  
pp. 317-338 ◽  
Author(s):  
Hugh P. Taylor
Keyword(s):  
Large Scale ◽  
Wide Spectrum ◽  
Volcanic Field ◽  
Parent Material ◽  
Rock Interaction ◽  
Metasedimentary Rocks ◽  
Clear Cut ◽  
End Members ◽  
Type 3

ABSTRACTOxygen isotope data are very useful in determining the source rocks of granitic magmas, particularly when used in combination with Sr, Pb, and Nd isotope studies. For example, unusually high δ18O values in magmas (δ18O> +8) require the involvement of some precursor parent material that at some time in the past resided on or near the Earth's surface, either as sedimentary rocks or as weathered or hydrothermally altered rocks. The isotopic systematics which are preserved in the Mesozoic and Cenozoic batholiths of western North America can be explained by grand-scale mixing of three broadly defined end-members: (1) oceanic island-arc magmas derived from a “depleted” (MORB-type?) source in the upper mantle (δ18O c. +6 and 87Sr/86Sr c. 0·703); (2) a high-18O (c. +13 to +17) source with a very uniform 87Sr/86Sr (c. 0·708 to 0·712), derived mainly from eugeosynclinal volcanogenic sediments and (or) hydrothermally altered basalts; and (3) a much more heterogeneous source (87Sr/86Sr c. 0·706 to 0·750, or higher) with a high δ18O (c. +9 to +15) where derived from supracrustal metasedimentary rocks and a much lower δ18O (c. +7 to +9) where derived from the lower continental crust of the craton. These end-members were successively dominant from W to E, respectively, within three elongate N–S geographic zones that can be mapped from Mexico all the way N to Idaho.18O/16O studies (together with D/H analyses) can, however, play a more important and certainly a unique role in determining the origins of the aqueous fluids involved in the formation of granitic and rhyolitic magmas. Fluid-rock interaction effects are most clear-cut when low-18O, low-D meteoric waters are involved in the isotopic exchange and melting processes, but the effects of other waters such as seawater (with a relatively high δD c. 0) can also be recognised. Because of these hydrothermal processes, rocks that ultimately undergo partial melting may exhibit isotopic signatures considerably different from those that they started with. We discuss three broad classes of potential source materials of such “hydrothermal-anatectic” granitic magmas, based mainly on water/rock (w/r), temperature (T), and the length of time (t) that fluid-rock interaction proceeds: (Type 1) epizonal systems with a wide variation in whole-rock δ18O and extreme 18O/16O disequilibrium among coexisting minerals (e.g. quartz and feldspar); (Type 2) deeper-seated and (or) longer-lived systems, also with a wide spectrum of whole-rock δ18O, but with equilibrated 18O/16O ratios among coexisting minerals; (Type 3) thoroughly homogenised and equilibrated systems with relatively uniform δ18O in all lithologies. Low-18O magmas formed by melting of rocks altered in a Type 2 or a Type 3 meteoric-hydrothermal system are the only kinds of “hydrothermal-anatectic” granitic magmas that are readily recognisable in the geological record. Analogous effects produced by other kinds of aqueous fluids may, however, be quite common, particularly in areas of extensional tectonics and large-scale rifting. The greatly enhanced permeabilities in such fractured terranes make possible the deep convective circulation of ground waters and sedimentary pore fluids. The nature and origin of low-18O magmas in the Yellowstone volcanic field and the Seychelles Islands are briefly reviewed in light of these concepts, as is the development of high-D, peraluminous magmas in the Hercynian of the Pyrenees.

scholarly journals Geochemical and Sr–Nd isotopic constraints on the petrogenesis and geodynamic significance of the Jebilet magmatism (Variscan Belt, Morocco)

2013 ◽  
Vol 151 (4) ◽  
pp. 666-691 ◽  
Author(s):  
ABDERRAHIM ESSAIFI ◽  
SCOTT SAMSON ◽  
KATHRYN GOODENOUGH
Keyword(s):  
Partial Melting ◽  
Wall Rock ◽  
Ultramafic Rocks ◽  
Isotopic Ratios ◽  
Isotopic Signatures ◽  
Plate Convergence ◽  
Metasedimentary Rocks ◽  
Microgranular Enclaves ◽  
Crustal Origin ◽  
Shallow Crust

AbstractIn the Variscan fold belt of Morocco, the Jebilet massif is characterized by Palaeozoic metasedimentary rocks intruded by syntectonic magmatism that includes an ultramafic–granitoid bimodal association and peraluminous granodiorites emplacedc. 330 Ma, intruded by younger leucogranitesc. 300 Ma. The mafic–ultramafic rocks belong to a tholeiitic series, and display chemical and isotopic signatures consistent with mixing between mantle-derived and crust-derived magmas or assimilation and fractional crystallization. The granites within the bimodal association are mainly metaluminous to weakly peraluminous microgranites that show characteristics of A2-type granites. The peraluminous, calc-alkaline series consists mainly of cordierite-bearing granodiorites enclosing magmatic microgranular enclaves and pelitic xenoliths. Detailed element and isotope data suggest that the alkaline and the peraluminous granitoids were formed in the shallow crust (<30 km) by partial melting of tonalitic sources at high temperatures (up to 900°C) and by partial melting of metasedimentary protoliths at relatively low temperatures (c. 750°C), respectively. Mixing between the coeval mantle-derived and crust-derived magmas contributed to the large variation of initial εNdvalues and initial Sr isotopic ratios observed in the granitoids. Further contamination occurred by wall-rock assimilation during ascent of the granodioritic plutons to the upper crust. The ultramafic–granitoid association has been intruded by leucogranites that have high initial Sr isotopic ratios and low initial εNdvalues, indicating a purely crustal origin. The heating events that caused emplacement of the Jebilet magmatism are related to cessation of continental subduction and convective erosion/thinning of the lithospheric mantle during plate convergence.

Melt-wall rock interaction in the mantle shown by silicate melt inclusions in peridotite xenoliths from the central Pannonian Basin (western Hungary)

Island Arc ◽  
2009 ◽  
Vol 18 (2) ◽  
pp. 375-400 ◽  
Author(s):  
Csaba Szabó ◽  
Károly Hidas ◽  
Enikő Bali ◽  
Zoltán Zajacz ◽  
István Kovács ◽  
...  
Keyword(s):  
Melt Inclusions ◽  
Pannonian Basin ◽  
Wall Rock ◽  
Silicate Melt ◽  
Rock Interaction ◽  
Peridotite Xenoliths

Protracted fluid–rock interaction in the Mesoarchaean and implication for gold mineralization: Example from the Warrawoona syncline (Pilbara, Western Australia)

2008 ◽  
Vol 272 (3-4) ◽  
pp. 639-655 ◽  
Author(s):  
Nicolas Thébaud ◽  
Pascal Philippot ◽  
Patrice Rey ◽  
Joël Brugger ◽  
Martin Van Kranendonk ◽  
...  
Keyword(s):  
Western Australia ◽  
Gold Mineralization ◽  
Rock Interaction
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