581 research outputs found
Zonation of Sulfate and Sulfide Minerals and Isotopic Composition in the Far Southeast Porphyry and Lepanto Epithermal CuâAu Deposits, Philippines
The worldâclass Far Southeast (FSE) porphyry system, Philippines, includes the FSE CuâAu porphyry deposit, the Lepanto CuâAu highâsulfidation deposit and the VictoriaâTeresa AuâAg intermediateâsulfidation veins, centered on the intrusive complex of dioritic composition. The Lepanto and FSE deposits are genetically related and both share an evolution characterized by early stage 1 alteration (deep FSE potassic, shallow Lepanto advanced argillicâsilicic, both at ~1.4 Ma), followed by stage 2 phyllic alteration (at ~1.3 Ma); the dominant ore mineral deposition within the FSE porphyry and the Lepanto epithermal deposits occurred during stage 2. We determined the chemical and S isotopic composition of sulfate and sulfide minerals from Lepanto, including stage 1 alunite (12 to 28 permil), aluminumâphosphateâsulfate (APS) minerals (14 to 21 permil) and pyrite (â4 to 2 permil), stage 2 sulfides (mainly enargiteâluzonite and some pyrite, â10 to â1 permil), and late stage 2 sulfates (barite and anhydrite, 21 to 27 permil). The minerals from FSE include stage 2 chalcopyrite (1.6 to 2.6 permil), pyrite (1.1 to 3.4 permil) and anhydrite (13 to 25 permil). The wholeârock S isotopic composition of weakly altered synâmineral intrusions is 2.0 permil.Stage 1 quartzâaluniteâpyrite of the Lepanto lithocap, above about 650 m elevation, formed from acidic condensates of magmatic vapor at the same time as hypersaline liquid formed potassic alteration (biotite) near sea level. The S isotopic composition of stage 1 aluniteâpyrite record temperatures of approximately 300â400°C for the vapor condensate directly over the porphyry deposit; this cooled to <250°C as the acidic condensate flowed to the NW along the Lepanto fault where it cut the unconformity at the top of the basement. Stage 1 alunite at the base of the advanced argillic lithocap over FSE contains cores of APS minerals with Sr, Ba and Ca; based on backâscattered electron images and ion microprobe data, these APS minerals show a large degree of chemical and Sâisotopic heterogeneity within and between samples. The variation in S isotopic values in these finely banded stage 1 alunite and APS minerals (16 permil range), as well as that of pyrite (6 permil range) was due largely to changes in temperature, and perhaps variation in redox conditions (average ~ 2:1 H2S:SO4). Such fluctuations could have been related to fluid pulses caused by injection of mafic melt into the diorite magma chamber, supported by mafic xenoliths hosted in diorite of an earlier intrusion.The S isotopic values of stage 2 minerals indicate temperatures as high as 400°C near sea level in the porphyry deposit, associated with a relatively reduced fluid (~10:1 H2S:SO4) responsible for deposition of chalcopyrite. Stage 2 fluids were relatively oxidized in the Lepanto lithocap, with an H2S:SO4 ratio of about 4. The oxidation resulted from cooling, which was caused by boiling during ascent and then dilution with steamâheated meteoric water in the lithocap. This cooling also resulted in the sulfidation state of minerals increasing from chalcopyrite stability in the porphyry deposit to that of enargite in the lithocapâhosted highâsulfidation deposit. The temperature at the base of the lithocap during stage 2 was â„300°C, cooling to <250°C within the main lithocap, and about 200°C towards the limit of the Lepanto orebody, approximately 2 km NW of the porphyry deposit. Approximate 300°C and 200°C isotherms, estimated from S isotopic and fluid inclusion temperatures during stage 1 and stage 2, shifted towards the core of the FSE porphyry deposit with time. This general retreat in isotherms was more than 500 m laterally within Lepanto and 500 m vertically within FSE as the magmaticâhydrothermal system evolved and collapsed over the magmatic center. During this evolution, there is also evidence recorded by large S isotopic variations in individual crystals for sharp pulses of higher temperature, relatively reduced fluid injected into the porphyry deposit.The worldâclass Far Southeast (FSE) porphyry system, Philippines, formed at 1.4â1.3 Ma and includes the linked FSE CuâAu porphyry and Lepanto CuâAu highâsulfidation deposits. Stageâ1 vapor condensate and quartzâaluniteâpyrite of the shallow Lepanto lithocap formed at the same time as hypersaline liquid created potassic alteration in the deeper porphyry, with Sâisotopic composition indicating temperatures of 300â400°C directly over the porphyry deposit and <250°C at the distal extent of the lithocap. The Sâisotopic composition of stageâ2 minerals indicate a temperature â€400°C in the porphyry deposit, associated with white mica alteration and chalcopyrite deposition from a relatively reduced fluid (âŒ10:1 H2S/SO4), whereas more oxidized conditions (âŒ4:1 H2S/SO4) at shallower depth were caused by cooling (deep boiling followed by shallow dilution with steamâheated liquid to âŒ200°C) during lithocapâhosted enargite deposition.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136455/1/rge12127_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136455/2/rge12127.pd
HÄllbar fysisk planering mot vattennÀra effekter av klimatförÀndringar - En studie om tvÄ kommuners arbete med skydd mot stigande havsnivÄer
This essay aims to investigate the physical planning practices that two Swedish municipalities are undertaking to protect themselves from rising sea-levels as an effect of global climate change. The physical planning practices undertaken by the municipalities will then be investigated regarding the three sustainability aspects (ecological, economic, social). The study will investigate if all aspects are prioritized equally or which aspect is regarded higher by each municipality. The two municipalities that this study focuses on are Kristianstad- and Vellinge municipality, with extra focus on the city of Kristianstad and FalsterbonÀset within each municipality. Despite different the geographical locations of the areas and the different preconditions that follow the two municipalities use similar defense practices as part of their physical planning, and the concept of sustainability is a constant reminder in the work of both municipalities. One aspect of sustainability is prioritized more by both municipalities however, and true sustainable development is difficult to achieve when planning for rising sea-levels
Magmatic contributions to hydrothermal systems
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95694/1/eost9233.pd
High-Grade Copper and Gold Deposited During Postpotassic Chlorite-White Mica-Albite Stage in the Far Southeast Porphyry Deposit, Philippines
Ninety-eight underground diamond holes (~102 km) drilled by Far Southeast Gold Resources Inc. at the Far Southeast porphyry Cu-Au deposit, Philippines, from 2011 to mid-2013, provide a three-dimensional exposure of the deposit between 700- and â750-m elevation, with surface at ~1,400-m elevation. Far Southeast contains an inferred resource of 891.7 million tonnes (Mt) averaging 0.7 g/t Au and 0.5 wt % Cu, equivalent to 19.8 Moz Au and 4.5 Mt Cu. This contribution reports the spatial and temporal distribution of alteration and mineralization at Far Southeast, notably a white-micaâchlorite-albite assemblage that formed after early secondary biotite and before late quartzâwhite-micaâpyrite alteration and that is associated with the highest copper and gold grades.
Alteration assemblages were determined by drill core logging, short-wavelength infrared (SWIR) spectral analysis, petrographic examination, and a quantitative evaluation of materials by scanning electron microscopy (QEMSCAN) study. Alteration is limited around sparse veins or pervasive where vein density is high and the alteration halos coalesce. The alteration and mineralization zones with increasing depth are as follows: (1) the lithocap of quartz-aluniteâdominated advanced argillic-silicic alteration that hosts part of the Lepanto high-sulfidation Cu-Au epithermal deposit (mostly above ~700-m elevation), (2) an aluminosilicate-dominated zone with coexisting pyrophyllite-diaspore ± kandite ± alunite and white mica (~700- to ~100-m elevation), (3) porphyry-style assemblages characterized by stockwork veins (below ~500-m elevation), (4) the 1 wt % Cu equivalent ore shell (~400- to â300-m elevation), and (5) an underlying subeconomic zone (about â300- to â750-m elevation, the base of drilling). The ore shells have a typical bell shape centered on a dioritic intrusive complex.
The paragenetic sequence of the porphyry deposit includes stage 1 granular gray to white quartz-rich (± anhydrite ± magnetite ± biotite) veins with biotite-magnetite alteration. These were cut by stage 2 lavender-colored euhedral quartz-rich (± anhydrite ± sulfides) veins, with halos of greenish white-micaâchlorite-albite alteration. The white mica is largely illite, with an average 2,203-nm Al-OH wavelength position. The albite may reflect the mafic nature of the diorite magmatism. The quartz veins of this stage are associated with the bulk of copper deposited as chalcopyrite and bornite, as well as gold. Thin Cu sulfide (chalcopyrite, minor bornite) veins with minor quartz and/or anhydrite (paint veins), with or without a white-mica halo, also occur. These veins were followed by stage 3 anhydrite-rich pyrite-quartz veins with white-mica (avg 2,197 nm, illite)âpyrite alteration halos.
Combined with previous studies, we conclude that this porphyry system, including the Far Southeast porphyry and Lepanto high-sulfidation Cu-Au deposits, evolved over a period of 0.1â0.2 m.y. Three diorite porphyry stocks were emplaced, and by ~1.4 Ma biotite-magnetiteâstyle alteration formed with quartz-anhydrite veins and deposition of â€0.5% Cu and â€0.5 g/t Au (stage 1); coupled with this alteration style, a barren lithocap of residual quartz with quartz-alunite halo plus kandite ± pyrophyllite and/or diaspore formed at shallower depth (>700-m elevation). Subsequently, lavender quartz and anhydrite veins with bornite and chalcopyrite (high-grade stage, avg ~1 wt % Cu and ~1 g/t Au) and white-micaâchlorite-albite halos formed below ~400-m elevation (stage 2). They were accompanied by local pyrite replacement, the formation of hydrothermal breccias and Cu sulfide (paint) veins. Stage 2 was followed at ~1.3 Ma by the formation of igneous breccias largely along the margins of the high-grade zones and stage 3 pyrite-quartz-anhydrite ± chalcopyrite veins with white-mica (mostly illitic) halos. At shallower depths in the transition to the base of the lithocap, cooling led to the formation of aluminosilicate minerals (mainly pyrophyllite ± diaspore ± dickite) with anhydrite plus high-sulfidation-state sulfides and pyrite veinlets. Consistent with previous studies, it is likely that the lithocap-hosted enargite-Au mineralization formed during this later period
Geochemistry of As-, F- and B-bearing waters in and around San Antonio de los Cobres, Argentina, and implications for drinking and irrigation water quality
Spring, stream and tap waters from in and around San Antonio de los Cobres, Salta, Argentina, were sampled to characterize their geochemical signatures, and to determine whether they pose a threat to human health and crops. The spring waters are typical of geothermal areas world-wide, in that they are Na-Cl waters with high concentrations of Astot, As(III), Li, B, HCO3, F and SiO2 (up to 9.49, 8.92, 13.1, 56.6, 1250, 7.30 and 57.2 mg L-1, respectively), and result from mixing of deep Na-Cl brines and meteoric HCO3-rich waters. Springs close to the town of San Antonio have higher concentrations of all elements, and are generally cooler, than springs in the Baños de Agua Caliente. Spring water chemistry is a result of mixing of deep Na-Cl brines and meteoric HCO3 waters. Stream waters are also Na-Cl type, and receive large inputs of all elements from the springs near San Antonio, but concentrations decrease downstream through the town of San Antonio due to mineral precipitation. The spring that is used as a drinking water source, and other springs in the area, have As, F and B concentrations in excess of WHO and Argentinian drinking water guidelines. Evaluation of the waters for irrigation purposes suggests that their high salinities and B concentrations may adversely affect crops. The waters may be improved for drinking and irrigation by dilution with cleaner meteoric waters, mineral precipitation or by use of commercial filters. Such recommendations could also be followed by other settlements that draw drinking and irrigation waters from geothermal sources
âŽâ°Ar/ÂłâčAr geochronology, fluid inclusions, and oreâgrade distribution of the Jiawula AgâPbâZn deposit, NE China: implications for deposit genesis and exploration
The Jiawula AgâPbâZn deposit is located in the northern part of the Great Xing'an Range metallogenic belt within the eastern segment of the Central Asian Orogenic Belt. Here, we report results from muscovite âŽâ°Ar/ÂłâčAr geochronology and fluid inclusion study and formulate a vertical projection map of the ore grade in this deposit. The muscovite from the Jiawula deposit yields a plateau age of 133.27 ± 0.66 Ma and a âŽâ°Ar/ÂłâčAr isochron age of 131.88 ± 0.83 Ma. The muscovite âŽâ°Ar/ÂłâčAr data indicate a discrete second hydrothermal event postdating the mineralization, which we correlate with postâcollisional extension after the subduction direction of the PalaeoâPacific Plate changed. Lowâsalinity aqueous fluid inclusions in quartz from the Jiawula deposit represent meteoric water or groundwater. Based on the fluid inclusion study, the fluids were trapped during cooling and decompression, which may have resulted in metal precipitation. We envisage that the copper precipitated from a highâtemperature fluid in the southern domain whereas lead, zinc, and silver precipitated at a lower temperature in the north. The spatial distribution of the oreâforming elements, therefore, reflects the ore fluid migrationâcooling path from the south to north
Rare earth element abundances in hydrothermal fluids from the Manus Basin, Papua New Guinea : indicators of sub-seafloor hydrothermal processes in back-arc basins
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 74 (2010): 5494-5513, doi:10.1016/j.gca.2010.07.003.Rare earth element (REE) concentrations are reported for a large suite of seafloor vent fluids
from four hydrothermal systems in the Manus backâarc basin (Vienna Woods, PACMANUS,
DESMOS and SuSu Knolls vent areas). Sampled vent fluids show a wide range of absolute REE
concentrations and chondriteânormalized (REEN) distribution patterns (LaN/SmN ~ 0.6 â 11;
LaN/YbN ~ 0.6 â 71; EuN/Eu*N ~ 1 â 55). REEN distribution patterns in different vent fluids range
from lightâREE enriched, to midâ and heavyâREE enriched, to flat, and have a range of positive
Euâanomalies. This heterogeneity contrasts markedly with relatively uniform REEN distribution
patterns of midâocean ridge hydrothermal fluids. In Manus Basin fluids, aqueous REE
compositions do not inherit directly or show a clear relationship with the REE compositions of
primary crustal rocks with which hydrothermal fluids interact. These results suggest that the
REEs are less sensitive indicators of primary crustal rock composition despite crustal rocks being
the dominant source of REEs in submarine hydrothermal fluids. In contrast, differences in
aqueous REE compositions are consistently correlated with differences in fluid pH and ligand
(chloride, fluoride and sulfate) concentrations. Our results suggest that the REEs can be used as
an indicator of the type of magmatic acid volatile (i.e., presence of HF, SO2) degassing in
submarine hydrothermal systems. Additional fluid data suggest that near seafloor mixing
between highâtemperature hydrothermal fluid and locally entrained seawater at many vent areas
in the Manus Basin causes anhydrite precipitation. Anhydrite effectively incorporates REE and
likely affects measured fluid REE concentrations, but does not affect their relative distributions.This study received financial support from the Ocean
Drilling Program Schlanger Fellowship (to P.R. Craddock), the WHOI Deep Ocean Exploration
Institute Graduate Fellowship (to E. Reeves) and NSF grant OCEâ0327448
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