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Mineral District (mineral + district)

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Earth and Environmental Science	100%

Selected Abstracts

Baguio Mineral District: An oceanic arc witness to the geological evolution of northern Luzon, Philippines

ISLAND ARC, Issue 4 2008
Graciano P. Yumul Jr
Abstract The Baguio Mineral District exposes rock formations that evince the geological and tectonic evolution of this district from a subduction-related marginal basin to an island arc setting. Available onshore and offshore data are consistent with an Early (onset phase) to Middle (developed phase) Miocene arc polarity reversal from the east (termination of subduction along the proto-East Luzon Trough) to the west (initiation of subduction along the Manila Trench). Geophysical modeling and geochemical data calculation showed a 30 ± 5 km crustal thickness for the mineral district. Subduction-related multiple arc magmatism and ophiolite accretion contributed to crustal thickening. Recent information on the Oligo,Miocene Zigzag and Klondyke formations in the mineral district reveal that the marginal basin, where these rocks were deposited, has received eroded materials from adjacent terrains characterized by siliceous lithologies. Furthermore, adakitic rocks, high permeable zones and extensional zones which are exploration markers applied to identify possible mineralization targets, are prevalent in the mineral district. The geological evolution that the district had undergone mimics the evolution of island arcs worldwide in general and northern Luzon in particular. [source]

Mineral Paragenesis of the Lepanto Copper and Gold and the Victoria Gold Deposits, Mankayan Mineral District, Philippines

RESOURCE GEOLOGY, Issue 2 2001
Rene Juna R. CLAVERIA
Abstract: Mineral paragenesis of the alteration, ore and gangue minerals of the Lepanto epithermal copper-gold deposit and the Victoria gold deposit, Mankayan Mineral District, Northern Luzon, Philippines, is discussed. The principal ore minerals of the Lepanto copper-gold deposit are enargite and luzonite, with significant presence of tennantite-tetrahedrite, chalcopyrite, sphalerite, galena, native gold/electrum and gold-silver tellurides. Pervasive alteration zonations are commonly observed from silicification outward to advanced argillic then to propylitic zone. The ore mineralogy of the Lepanto copper-gold deposit suggests high fS2 in the early stages of mineralization corresponding to the deposition of the enargite-luzonite-pyrite assemblage. Subsequent decrease in the fS2 formed the chalcopyrite-tennantite-pyrite assemblage. An increase in the fS2 of the fluids with the formation of the covellite-digenite-telluride assemblage caused the deposition of native gold/electrum and gold-silver tellurides. The principal ore minerals of the Victoria gold deposit are sphalerite, galena, chalcopyrite, tetrahedrite and native gold/electrum. The alteration halos are relatively narrow and in an outward sequence from the ore, silica alteration grades to illitic-argillic alteration, which in turn grades to propylitic alteration. The Victoria gold mineralization has undergone early stages of silica supersaturation leading to quartz deposition. Vigorous boiling increased the pH of the fluids that led to the deposition of sulfides and carbonates. The consequent decrease in H2S precipitated the gold. Gypsum and anhydrite mainly occur as overprints that cut the carbonate-silica stages. The crosscutting and overprinting relationships of the Victoria quartz-gold-base metal veins on the Lepanto copper-gold veins manifest the late introduction of near neutral pH hydrothermal fluids. [source]

Stable Isotope Study of the Langshan Polymetallic Mineral District, Inner Mongolia, China

RESOURCE GEOLOGY, Issue 1 2000
Ping DING
The lead isotope study shows that these deposits were probably formed from 2. 0 to 1. 5 Ga, and were deformed and metamorphosed 1. 45 Ga. Ore lead could be a mixture of mantle lead and crustal lead. The C and S isotope results indicate that these deposits were precipitated in closed or semi-closed rift basins, and the source of sulfur might be Proterozoic ocean sulfate. The H and O isotope results indicate that the ,D and ,18O values of rocks were changed by water-rock interaction during metamorphism and hydrothermal alteration. The scale of ,D and ,18O shift of rocks reflects the grade of metamorphism and alteration as well as the water-rock ratios. However, the water-rock ratios in the metamorphic processes of Langshan mineral district were relatively low, and the source of water during metamorphism is suggested to be ancient meteoric water. Based on isotopic results and the geological background, it is concluded that these deposits may belong to Proterozoic sedimentary exhalative (SEDEX) type. [source]

Stress behavior from fault data sets within a transtensional zone, South Central Cordillera, Luzon, Philippines: Implications for mineral occurrences

ISLAND ARC, Issue 1 2009
Mario A. Aurelio
Abstract The structural signature in the area between the Baguio mineral district and Ansagan, Tuba, Benguet in the South Central Cordillera, northern Luzon, Philippines, is dominated by northeast- to ENE-trending faults, contained within a NNW,SSE-trending transtensional strip. This 50-km-long, 25-km-wide elongated tectonic zone is bounded to the west by the Pugo Fault and to the east by the Tebbo Fault, both being branches of the Philippine Fault System. Detailed structural geological (particularly microtectonic) analysis of fracture and mineral vein systems indicates strong conformity with the regional structural direction. Computed extensional stress axis ,3 directions are oriented N150° on average, sub-parallel to the strike of the bounding faults. The existence of known mineral deposits and prospects within the tectonic strip implies an intimate relationship between transtension and mineral occurrence. [source]

Baguio Mineral District: An oceanic arc witness to the geological evolution of northern Luzon, Philippines

Carlin-type Gold Prospects in Surigao del Norte, Mindanao Island, Philippines: Their Geology and Mineralization Potential

RESOURCE GEOLOGY, Issue 3 2005
Victor B. Maglambayan
Abstract. Three calcareous sedimentary rock-hosted Carlin type-like gold prospects were mapped in a mineral production sharing agreement area of Philex Gold Philippines Inc. in Taganaan municipality, Surigao del Norte province in Mindanao island in the Philippines. They occur along a 20,25 km long trend of known epigenetic gold and porphyry copper deposits that lie close to several splays of the Philippine Fault Zone. The gold district forms part of the Late Cretaceous Eastern Mindanao Range that hosts early Paleogene and late Pliocene to Quaternary intrusive rocks. Gold is invisible in the jasperoid outcrops in Lascogon, Napo, and Danao prospects. The jasperoids occur in lenses of marls belonging to the Taganaan Marl Member that is associated to a turbiditic member of the Middle Miocene Mabuhay Formation. The marl lenses include gently dipping interbedded silty limestones and calcareous shales. The "invisible gold" mineralization in silicified calcareous rocks resembles Carlin-type deposits. Based on the mapped igneous and sedimentary rocks, a possible heat source for the gold mineralization is either or both of the two main phases of intrusion, Mabuhay An-desite or Alipao Andesite Porphyry. Forty-eight rock samples, fifteen stream sediment samples, and one soil sample were critical in delineating the general features of the potential Carlin-type prospects. The gold grades of jasperoids in the three prospects range from trace amounts to 20 g/t Au. Regional studies of gold and porphyry copper mineralization in the Surigao del Norte mineral district are important in delineating ore targets for drilling in the three prospects. [source]

Hydrothermal Alteration and Cu-Au Mineralization at Nena High Sulfidation-type Deposit, Frieda River, Papua New Guinea

RESOURCE GEOLOGY, Issue 4 2002
Joseph Onglo Espi
Abstract. The Nena Cu-Au deposit, located in the Frieda River mineral district of northwestern mainland Papua New Guinea, is a composite structurally-lithologically controlled high sulfidation (HS) system. Its hydrothermal alteration and Cu-Au mineralization are presented in this paper. Initially propylitized andesitic volcanics veined by epithermal quartz were pervasively superimposed by zoned HS alteration. The zonation grades from vuggy silica core to sulfur-rich, pyritic silica-alunite halo followed by pyrophyllite-dickite-kaolinite interval and finally to thin illite-smectite margin, suggesting progressive decrease in temperature and increase in pH. This zonation is enveloped by chlorite-epidote-calcite-gypsum alteration. The acid altered rocks were then invaded by multiple phases of pyrite, subsequently crosscut by quartz, vein alunite and barite. Then sequential deposition of bladed covellite, enargite, luzonite and stibioluzonite occurred from the NW to the SE portions of the deposit, forming a zonation suggestive of progressive decrease in temperature, sulfur fugacity and sulfidation stage. Most ore mineralization occurs in the vuggy silica core. Gold mineralization commenced from the transition of enargite to luzonite and continued throughout the stibioluzonite stage. Associated with gold deposition are Au-rich pyrite, tennantite-tetrahedrite, chalcopyrite-bornite, native tellurium, electrum, calaverite, bismuthinite and galena. Native sulfur occupied the remaining cavities and represents the waning stage of the hydrothermal system. Fluid inclusions studies distinguished magmatic (>300,350d,C, 9,15 wt% NaCl equiv.) and meteoric (<150,200d,C, 1,2 wt% NaCl equiv.) fluids (Holzberger et al., 1996). Temperatures and salinities of fluid inclusions from barite associated with Cu sulfides show a general decrease from NW (330d,C, 9,15 wt% NaCl equiv.) to SE (172d,C, 10 wt% NaCl equiv.) parts of the deposit, indicating gradual entrainment of ground water (Hitchman and Espi, 1997). Interaction of magmatic fluids with meteoric water accompanied by changes in temperature, salinity, acidity and oxidation state of the resultant fluids is interpreted to have been the main cause of metal precipitation. Finally, supergene processes generated Au zone with an underlying chalcocite-covellite-digenite blanket over the primary sulfides at depth. Gold occurs as lattice constituent in scorodite, limonite-goethite and jarosite. Chalcocite is more abundant and widespread than other Cu sulfides. Acidic fluids deposited powdery alunite and kaolinite, vein alunite and amorphous silica. Weakly secondary biotite-quartz altered porphyry located below the known HS Cu-Au deposit contains chalcopyrite-bornite and is overprinted by quartz-alunite-pyro-phyllite-pyrite assemblage. This feature indicates close temporal, spatial and genetic relation between the two deposit types. [source]