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CURATOR
A pinboard by
JOSEPH AISABOKHAE

I am a PhD. student in Applied Geophysics. I employ geophysical methods in exploring for minerals

PINBOARD SUMMARY

Geophysical delineation of auriferous structures using electromagnetic and chargeability surveys

Primary gold mineralization predominantly occur in quartz veins within several lithologies including schist belts comprised of fine grained mica schist, amphibolite schist and several varieties of gneisses. In Nigeria, the schist belts are best developed in the western part of the country and cut across major parts of Kebbi State within the Precambrian Basement Complex with the presence of shear zones acting as channels for hydrothermal fluid deposition. Gold bearing alteration zones and associated quartz veins formed in local extension sites are centered on well-defined fractures and faults in host rocks. This research serves to integrate electromagnetic and chargeability prospecting methods to delineate and map subsurface fractured zones and faults (Latitude 10° 46ˈ- 10° 48ˈ and Longitude 4° 48ˈ- 4°50ˈ) which are relays of continental-scale trans-current faults or deep tapping crustal faults hosting gold-mineralized quartz veins along the regional shear zone system. The outcome of the study will inform policy and decision makers, investors, as well as other stakeholders in the mining sector about the superfluity of this precious mineral in the survey area.

11 ITEMS PINNED

Multistage gold mineralization in the Wa-Lawra greenstone belt, NW Ghana: The Bepkong deposit

Abstract: The Bepkong gold deposit is one of several gold camps in the Paleoproterozoic Wa-Lawra greenstone belt in northwest Ghana. These deposits lay along the Kunche-Atikpi shear zone, which is part of the larger transcurrent Jirapa shear zone. The formation of these shear zones can be attributed to the general ESE-WNW major shortening that took place in the Wa-Lawra belt. Gold mineralization in the Bepkong deposit mainly occurs within graphitic shales and volcaniclastic rocks. The ore consists of four N-S trending lenticular bodies, plunging steeply to the south, that are lithologically and structurally controlled. Their shape and thickness are variable, though a general strike length of 560 m and an overall thickness of 300 m can be defined. An alteration mineral assemblage characterises the ore, and consists of chlorite-calcite-sericite-quartz-arsenopyrite-pyrite. Pyrite, as distinct from arsenopyrite, is not limited to the altered rocks and occurs throughout the area. At Bepkong, gold is associated with arsenopyrite and pyrite, which occur disseminated in the mineralized wall rock, flanking Type-1 quartz veins, or within fractures crossing these veins. Textural observations indicate the early formation of abundant arsenopyrite, followed by pyrite, with chalcopyrite, galena, sphalerite and pyrrhotite occurring as inclusions within pyrite and altered arsenopyrite. Detailed petrography, coupled with SEM, LA-ICP-MS and EMP analyses, indicate that gold in the Bepkong deposit occurs in three distinct forms: (i) invisible gold, mostly in arsenopyrite (ii); visible gold as micron-size grains within fractures and altered rims of arsenopyrite, as well as at the interface of sulphide grains; (iii) free visible gold in fractures in quartz veins and their selvages. We interpret the invisible gold to have co-precipitated with the early-formed arsenopyrite. The small visible gold grains observed within the sulphide interfaces, altered arsenopyrite, fractures and grain boundaries, are interpreted to have formed as a result of the dissolution and redistribution of the invisible gold during later alteration of arsenopyrite, which took place at lower temperatures during crenulation and fracturing accompanying late deformation, and was accompanied by pervasive pyritization of the wall rock.

Pub.: 12 May '16, Pinned: 11 Aug '17

Constraints of fluid inclusions and in-situ S-Pb isotopic compositions on the origin of the North Kostobe sediment-hosted gold deposit, eastern Kazakhstan

Abstract: The North Kostobe gold deposit in the Kalba gold province, eastern Kazakhstan, is tectonically located in the Chara shear zone of the western Altaids. The Chara shear zone separates the Kazakhstan microcontinent and Siberia craton which collided in the late Carboniferous. In the North Kostobe deposit, Au mineralization is distributed along an E-W striking shear zone linked to the NW-SE trending regional faults, and is mainly concentrated in quartz-sulfide-carbonate veins or in disseminated sulfides hosted in carbonaceous metasedimentary rocks. Sulfide minerals are mainly pyrite and arsenopyrite, and were formed in three generations. The first generation is dominated by pyrite (py1) occurring as microcrystal aggregates, followed by the second generation including euhedral arsenopyrite and compact pyrite (py2) locally overgrowing early py1 grains as rims; third generation of pyrite (py3) is present in barren micro-fractures crosscutting early mineralized rocks. Native gold is present in cracks of brecciated arsenopyrite grains and as inclusions in py2. Investigations on fluid inclusions in auriferous quartz veins indicate that the ore-related fluids are CO2-bearing, with homogenization temperatures of 288 °C and low salinity (1.42 to 8.03 wt% NaCl equiv). The fluids have calculated δ18O and δD values ranging from 9.96 to 11.86‰ and from − 75 to − 97.1‰, respectively, suggesting that they were most likely metamorphic in origin.

Pub.: 15 Oct '16, Pinned: 11 Aug '17

The Tasiast deposit, Mauritania

Abstract: The Tasiast gold deposits are hosted within Mesoarchean rocks of the Aouéouat greenstone belt, Mauritania. The Tasiast Mine consists of two deposits hosted within distinctly different rock types, both situated within the hanging wall of the west-vergent Tasiast thrust. The Piment deposits are hosted within metasedimentary rocks including metaturbidites and banded iron formation where the main mineral association consists of magnetite-quartz-pyrrhotite ± actinolite ± garnet ± biotite. Gold is associated with silica flooding and sulphide replacement of magnetite in the turbidites and in the banded iron formation units. The West Branch deposit is hosted within meta-igneous rocks, mainly diorites and quartz diorites that lie stratigraphically below host rocks of the Piment deposits. Most of the gold mineralisation at West Branch is hosted by quartz–carbonate veins within the sheared and hydrothermally altered meta-diorites that constitute the Greenschist Zone. At Tasiast, gold mineralisation has been defined over a strike length > 10 km and to vertical depths of 740 m. All of the significant mineralised bodies defined to date dip moderately to steeply (45° to 70°) to the east and have a south–southeasterly plunge. Gold deposits on the Tasiast trend are associated with second order shear zones that are splays cutting the hanging wall block of the Tasiast thrust. An age of 2839 ± 36 Ma obtained from the hydrothermal overgrowth on zircons from a quartz vein is interpreted to represent the age of mineralisation.

Pub.: 03 Sep '15, Pinned: 11 Aug '17

Pressure, temperature, and timing of mineralization of the sedimentary rock-hosted orogenic gold deposit at Klipwal, southeastern Kaapvaal Craton, South Africa

Abstract: Gold mineralization in the Klipwal Shear Zone (KSZ) at the Klipwal Gold Mine is confined to laminated quartz–carbonate lodes, stringers, and associated alteration in sandstone and siltstone of the Delfkom Formation in the upper Mozaan Group of the Mesoarchaean Pongola Supergroup. The moderately dipping brittle–ductile KSZ strikes N–S with an oblique–reverse, sinistral sense of shear. The deformational events that are recognized include an early compressional phase that produced anastomosing shears defined by shear fabrics with numerous shear-parallel laminated quartz–carbonate fault-fill veins and, in places, extensional quartz vein stockworks, and a late brittle reactivation phase that produced fault breccias, displacing earlier extensional veins. Three closely spaced economic reefs (lodes) are developed: the main R-reef constitutes the KSZ, while the J- and H-reefs represent footwall splays. Alteration comprises chlorite, muscovite, epidote, feldspar, and carbonates along with pyrite, arsenopyrite, and chalcopyrite ± pyrrhotite. An inner alteration zone is dominated by laminated quartz–carbonate veins with alternating quartz–carbonate-rich and muscovite–chlorite-rich laminae, whereas the proximal zone is characterized by alteration halos of K-feldspar, albite, epidote, chlorite, and muscovite along with carbonates and associated quartz veins. Chlorite thermometry from the inner and proximal zones yielded temperatures of 267 to 312 °C. Arsenopyrite compositions provide temperatures in the same range, 255 to 318 °C. Fluid inclusion microthermometry and Raman spectrometry of quartz veins in the mineralized reefs reveal the presence of metamorphogenic aqueous–gaseous fluid with an average salinity of 6.5 wt% NaCl equiv. Fluid compositions and estimated pressure–temperature (P–T) range (1.1 to 2.5 kbar at 255 to 318 °C) are typical of orogenic gold deposits. Devolatilization during the regional facies metamorphism of the Pongola Supergroup is considered the likely fluid-forming event with fluid flow focused into a “compressional jog” of the KSZ. Shear-induced pressure fluctuations generated a phase separation of the initial aqueous–gaseous fluid, producing a gaseous and low-salinity aqueous fluid. This, together with fluid–rock interaction, and a decrease in fO2 lead to sulfide and gold precipitation at Klipwal. Re-Os data from six sulfide samples constrain the age of sulfide precipitation and, by inference, gold mineralization, to 2563 ± 84 Ma, with an initial 187Os/188Os = 0.29 ± 0.08 (MSWD = 0.38). This age is distinctly younger than the post-Pongola granites (2863–2721 Ma), ruling out the association of granite emplacement with mineralization. This would suggest that mineralization is linked to the regional D3 folding event which reactivated the KSZ after emplacement of the post-Pongola granites and that final brittle, post-mineralization reactivation is related to Karoo age faulting. Low initial Os values suggest that ore fluid interacted with mafic rocks, leaching non-radiogenic Os, the likely source being the deeper seated Nsuze Group volcanics and/or the greenstone belts that underlie the Pongola Supergroup.

Pub.: 24 Jan '15, Pinned: 11 Aug '17

A Palaeoproterozoic multi-stage hydrothermal alteration system at Nalunaq gold deposit, South Greenland

Abstract: Abstract Nalunaq is an orogenic, high gold grade deposit situated on the Nanortalik Peninsula, South Greenland. Mineralisation is hosted in shear zone-controlled quartz veins, located in fine- and medium-grained amphibolite. The deposit was the site of Greenland’s only operating metalliferous mine until its closure in 2014, having produced 10.67 t of gold. This study uses a combination of field investigation, petrography and U/Pb zircon and titanite geochronology to define a multi-stage hydrothermal alteration system at Nalunaq. A clinopyroxene-plagioclase-garnet(-sulphide) alteration zone (CPGZ) developed in the Nanortalik Peninsula, close to regional peak metamorphism and prior to gold-quartz vein formation. The ca. 1783–1762-Ma gold-quartz veins are hosted in reactivated shear zones with a hydrothermal alteration halo of biotite-arsenopyrite-sericite-actinolite-pyrrhotite(-chlorite-plagioclase-löllingite-tourmaline-titanite), which is best developed in areas of exceptionally high gold grades. Aplite dykes dated to ca. 1762 Ma cross-cut the gold-quartz veins, providing a minimum age for mineralisation. A hydrothermal calcite-titanite alteration assemblage is dated to ca. 1766 Ma; however, this alteration is highly isolated, and as a result, its field relationships are poorly constrained. The hydrothermal alteration and mineralisation is cut by several generations of ca. 1745-Ma biotite granodiorite accompanied by brittle deformation. A ca. 1745-Ma lower greenschist facies hydrothermal epidote-calcite-zoisite alteration assemblage with numerous accessory minerals forms halos surrounding the late-stage fractures. The contrasting hydrothermal alteration styles at Nalunaq indicate a complex history of exhumation from amphibolite facies conditions to lower greenschist facies conditions in an orogenic belt which resembles modern Phanerozoic orogens.AbstractNalunaq is an orogenic, high gold grade deposit situated on the Nanortalik Peninsula, South Greenland. Mineralisation is hosted in shear zone-controlled quartz veins, located in fine- and medium-grained amphibolite. The deposit was the site of Greenland’s only operating metalliferous mine until its closure in 2014, having produced 10.67 t of gold. This study uses a combination of field investigation, petrography and U/Pb zircon and titanite geochronology to define a multi-stage hydrothermal alteration system at Nalunaq. A clinopyroxene-plagioclase-garnet(-sulphide) alteration zone (CPGZ) developed in the Nanortalik Peninsula, close to regional peak metamorphism and prior to gold-quartz vein formation. The ca. 1783–1762-Ma gold-quartz veins are hosted in reactivated shear zones with a hydrothermal alteration halo of biotite-arsenopyrite-sericite-actinolite-pyrrhotite(-chlorite-plagioclase-löllingite-tourmaline-titanite), which is best developed in areas of exceptionally high gold grades. Aplite dykes dated to ca. 1762 Ma cross-cut the gold-quartz veins, providing a minimum age for mineralisation. A hydrothermal calcite-titanite alteration assemblage is dated to ca. 1766 Ma; however, this alteration is highly isolated, and as a result, its field relationships are poorly constrained. The hydrothermal alteration and mineralisation is cut by several generations of ca. 1745-Ma biotite granodiorite accompanied by brittle deformation. A ca. 1745-Ma lower greenschist facies hydrothermal epidote-calcite-zoisite alteration assemblage with numerous accessory minerals forms halos surrounding the late-stage fractures. The contrasting hydrothermal alteration styles at Nalunaq indicate a complex history of exhumation from amphibolite facies conditions to lower greenschist facies conditions in an orogenic belt which resembles modern Phanerozoic orogens.

Pub.: 12 Jul '16, Pinned: 11 Aug '17

Mesothermal gold vein mineralization of the Samdong mine, Youngdong mining district, Republic of Korea

Abstract: Mesothermal gold mineralization at the Samdong mine (5.5–13.5 g/ton Au), Youngdong mining district, is situated in massive quartz veins up to 1.2 m wide which fill fault fractures within upper amphibolite to epidote-amphibolite facies, Precambrian-banded biotite gneiss. The veins are mineralogically simple, consisting of iron- and base-metal sulfides and electrum, and are associated with weak hydrothermal alteration zones (<0.5 m wide) characterized by silicification and sericitization. Fluid inclusion data and equilibrium thermodynamic interpretation of mineral assemblages indicate that the quartz veins were formed at temperatures between 425 and 190°C from relatively dilute aqueous fluids (4.5–13.8 wt. % equiv NaCl) containing variable amounts of CO2 and CH4. Evidence of fluid unmixing (CO2 effervescence) during the early vein formation indicates approximate pressures of 1.3–1.9 kbars, corresponding to minimum depths of ≈ 5–7 km under a purely lithostatic pressure regime. Gold deposition occurred mainly at temperatures between 345 and 240 °C, likely due to decreases in sulfur activity accompanying fluid unmixing. The δ34S values of sulfide minerals (-3.0 to 5.3 ‰), and the measured and calculated O-H isotope compositions of ore fluids (δ18O = 5.7 to 7.6‰; δ = −74 to −80‰) indicate that mesothermal gold mineralization at the Samdong mine may have formed from dominantly magmatic hydrothermal fluids, possibly related to intrusion of the nearby ilmenite-series, ‘Kimcheon Granite’ of Late Jurassic age.

Pub.: 01 Aug '95, Pinned: 11 Aug '17

Mineralogical, fluid inclusion, and stable isotope constraints on mechanisms of ore deposition at the Samgwang mine (Republic of Korea)—a mesothermal, vein-hosted gold–silver deposit

Abstract: The Samgwang mine is located in the Cheongyang gold district (Cheonan Metallogenic Province) of the Republic of Korea. It consists of eight massive, gold-bearing quartz veins that filled NE- and NW-striking fractures along fault zones in Precambrian granitic gneiss of the Gyeonggi massif. Their mineralogy and paragenesis allow two separate vein-forming episodes to be recognized, temporally separated by a major faulting event. The ore minerals occur in quartz and calcite of stage I, associated with fracturing and healing of veins. Hydrothermal wall-rock alteration minerals of stage I include Fe-rich chlorite (Fe/(Fe+Mg) ratios 0.74-0.81), muscovite, illite, K-feldspar, and minor arsenopyrite, pyrite, and carbonates. Sulfide minerals deposited along with electrum during this stage include arsenopyrite, pyrite, pyrrhotite, sphalerite, marcasite, chalcopyrite, galena, argentite, pyrargyrite, and argentian tetrahedrite. Only calcite was deposited during stage II. Fluid inclusions in quartz contain three main types of C–O–H fluids: CO2-rich, CO2–H2O, and aqueous inclusions. Quartz veins related to early sulfides in stage I were deposited from H2O–NaCl–CO2 fluids (1,500–5,000 bar, average 3,200) with Thtotal values of 200°C to 383°C and salinities less than about 7 wt.% NaCl equiv. Late sulfide deposition was related to H2O–NaCl fluids (140–1,300 bar, average 700) with Thtotal values of 110°C to 385°C and salinities less than about 11 wt.% NaCl equiv. These fluids either evolved through immiscibility of H2O–NaCl–CO2 fluids as a result of a decrease in fluid pressure, or through mixing with deeply circulated meteoric waters as a result of uplift or unloading during mineralization, or both. Measured and calculated sulfur isotope compositions (δ34SH2S = 1.5 to 4.8‰) of hydrothermal fluids from the stage I quartz veins indicate that ore sulfur was derived mainly from a magmatic source. The calculated and measured oxygen and hydrogen isotope compositions (δ18OH2O = −5.9‰ to 10.9‰, δD = −102‰ to −87‰) of the ore-forming fluids indicate that the fluids were derived from magmatic sources and evolved by mixing with local meteoric water by limited water–rock exchange and by partly degassing in uplift zones during mineralization. While most features of the Samgwang mine are consistent with classification as an orogenic gold deposit, isotopic and fluid chemistry indicate that the veins were genetically related to intrusions emplaced during the Jurassic to Cretaceous Daebo orogeny.

Pub.: 14 Oct '09, Pinned: 11 Aug '17