Overprinting porphyry‐type veinlets on the intrusive rocks and phreatomagmatic breccias in the Southwest prospect,southwestern Sto. Tomas II (Philex), Baguio District,Philippines     

Avriel Venis L. Cirineo  Akira Imai  Ryohei Takahashi  Redempta P. Baluda  Noel C. Oliveros  Victor B. Maglambayan  Roy Ronald C. Luis  Maria Lourdes M. Faustino  Jacky Almadin 《Resource Geology》2021,71(1):1-40

The Southwest prospect is located at the southwestern periphery of the Sto. Tomas II porphyry copper–gold deposit in the Baguio District, northwestern Luzon, Philippines. The Southwest prospect hosts a copper‐gold mineralization related to a complex of porphyry intrusions, breccia facies, and overlapping porphyry‐type veinlets emplaced within the basement Pugo metavolcanics rocks and conglomerates of the Zigzag Formation. The occurrences of porphyry‐type veinlets and potassic alteration hosted in the complex are thought to be indications of the presence of blind porphyry deposits within the Sto. Tomas II vicinity. The complex is composed of at least four broadly mineralogically similar dioritic intrusive rocks that vary in texture and alteration type and intensity. These intrusions were accompanied with at least five breccia facies that were formed by the explosive brecciation, induced by the magmatic–hydrothermal processes and phreatomagmatic activities during the emplacement of the various intrusions. Hydrothermal alteration assemblages consisting of potassic, chlorite–magnetite, propylitic and sericite–chlorite alteration, and contemporaneous veinlet types were developed on the host rocks. Elevated copper and gold grades correspond to (a) chalcopyrite–bornite assemblage in the potassic alteration in the syn‐mineralization early‐mineralization diorite (EMD) and contemporaneous veinlets and (b) chalcopyrite‐rich mineralization associated with the chalcopyrite–magnetite–chlorite–actinolite±sericite veinlets contemporaneous with the chlorite–magnetite alteration. Erratic remarkable concentrations of gold were also present in the late‐mineralization Late Diorite (LD). High X_Mg of calcic amphiboles (>0.60) in the intrusive rocks indicate that the magmas have been oxidizing since the early stages of crystallization, while a gap in the composition of Al between the rim and the cores of the calcic amphiboles in the EMD and LD indicate decompression at some point during the crystallization of these intrusive rocks. Fluid inclusion microthermometry suggests the trapping of immiscible fluids that formed the potassic alteration, associated ore mineralization, and sheeted quartz veinlets. The corresponding formation conditions of the shallower and deeper quartz veinlets were estimated at pressures of 50 and 30 MPa and temperatures of 554 and 436°C at depths of 1.9 and 1.1 km. Temperature data from the chlorite indicate that the chalcopyrite‐rich mineralization associated with the chlorite–magnetite alteration was formed at a much lower temperature (ca. 290°C) than the potassic alteration. Evidence from the vein offsetting matrix suggests multiple intrusions within the EMD, despite the K‐Ar ages of the potassic alteration in EMD and hornblende in the LD of about the same age at 3.5 ± 0.3 Ma. The K‐Ar age of the potassic alteration was likely to be thermally reset as a result of the overprinting hydrothermal alteration. The constrained K‐Ar ages also indicate earlier formed intrusive rocks in the Southwest prospect, possibly coeval to the earliest “dark diorite” intrusion in the Sto. Tomas II deposit. In addition, the range of δ³⁴S of sulfide minerals from +1.8‰ to +5.1‰ in the Southwest prospect closely overlaps with the rest of the porphyry copper and epithermal deposits in the Sto. Tomas II deposit and its vicinity. This indicates that the sulfides may have formed from a homogeneous source of the porphyry copper deposits and epithermal deposits in the Sto. Tomas II orebody and its vicinity. The evidence presented in this work proves that the porphyry copper‐type veinlets and the adjacent potassic alteration in the Southwest prospect are formed earlier and at a shallower level in contrast with the other porphyry deposits in the Baguio District.  相似文献   

Influence of friction on erosion and accretion processes in the Yavaros Bay,Gulf of California     

Noel Carbajal  Juan A. Dworak  Yovani Montaño-Ley  Cristina Noyola-Medrano 《Environmental Earth Sciences》2014,72(2):429-440

A two-dimensional, vertically integrated, nonlinear numerical model was applied to investigate the tide-driven bed load transport of sediments and morphodynamics in the shallow coastal lagoon of Yavaros, located in the southeastern part of the Gulf of California, Mexico. Satellite imagery exposes strong sediment dynamics in this coastal region. The dynamics in the lagoon were forced by 13 tidal constituents at the open boundary. Tides are of a mixed character and they are predominantly semidiurnal. The calculations showed areas of intense tidal currents and considerable water exchange with the Gulf of California. Numerical experiments revealed an ebb-dominant tidal distortion and a net export of sediment from the lagoon to the Gulf of California. A simulation of 20 years showed that the lagoon exported about 1,600 m³ of sediment; however, the daily oscillating exchange of sediment reached values of around 8 m³. The daily averaged flux of export–import sediments oscillates principally with semiannual, monthly and fortnightly periods. By applying a threshold velocity, a variable friction coefficient and the calculated amplitude of tidal velocities, it was possible to determine that morphological changes occur in zones of sharp topographic gradients and to explain the effect of friction on the export–import process of sediments. A 10-year simulation revealed that accumulation of sediment (~20 cm) occurred in small areas, whereas erosion occurred in larger areas but with less intensity (~8 cm). Besides the importance for the morphodynamics, these kinds of erosion–accretion processes may be relevant for the marine ecology.  相似文献   

AASG Introduction     

Noel Tyler 《Marine Georesources & Geotechnology》2013,31(2-3)

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Mapping rates associated with polygons     

Noel Cressie  Hal S. Stern  Deanne Reber Wright 《Journal of Geographical Systems》2000,2(1):61-69

Suppose that geographic data under investigation are rates associated with polygons. For example, disease incidence, mortality, and census undercount data may be displayed as rates. Spatial analysis of data of this sort can be handled very naturally through Bayesian hierarchical statistical modeling, where there is a measurement process at the first level, an explanatory process at the second level, and a prior probability distribution on unknowns at the third level. In our paper, we shall feature epidemiological data, specifically disease-incidence rates, and the “polygons” referred to in the title are typically states or counties.  相似文献   

An epeiric ramp: low-energy, cool-water carbonate facies in a Tertiary inland sea, Murray Basin, South Australia   总被引：1，自引：0，他引：1  

Jeff J. Lukasik  Noel P. James  Brian McGowran  & Yvonne Bone 《Sedimentology》2000,47(4):851-881

The Murray Supergroup records temperate‐water carbonate deposition within a shallow, mesotrophic, Oligo‐Miocene inland sea protected from high‐energy waves and swells of the open ocean by a granitic archipelago at its southern margin. Rocks are very well preserved and exposed in nearly continuous outcrop along the River Murray in South Australia. Most facies are rich in carbonate silt, contain a background assemblage of gastropods (especially turritellids) and infaunal bivalves, and are packaged on a decimetre‐scale defined by firmground and hardground omission surfaces. Bioturbation is pervasive and overprinted, resulting in rare preservation of physical sedimentary structures. Facies are grouped into four associations (large foraminiferan–bryozoan, echinoid–bryozoan, mollusc and clay facies) interpreted to represent shallow‐water (<50 m) deposition under progressively higher trophic resource levels (from low mesotrophy to eutrophy), and restricted marine conditions from relatively offshore to nearshore regions. A large‐scale shift from high‐ to low‐mesotrophic conditions within lower Miocene strata reflects a change in climate from wet to seasonally dry conditions and highlights the influence terrestrially derived nutrients had upon this shallow, land‐locked sea. Overall, low trophic resource levels during periods of seasonally dry climate resulted in a deepening of the euphotic zone, a widespread proliferation of foraminiferan photozoan fauna and a relatively high carbonate productivity. Inshore, heterozoan facies became progressively muddier and restricted towards the shoreline. In contrast, periods of wet climate led to rising trophic resource levels, resulting in a shallowing of the euphotic zone, a decrease in epifaunal and seagrass cover and widespread development of a mostly heterozoan biota dominated by infaunal echinoids. Rates of carbonate production and accumulation were relatively low. The Murray Basin is best described as an epeiric ramp. Wide facies belts developed in a shallow sea on a low‐angled slope reaching many hundreds of kilometres in length. Grainy shoal and back‐barrier facies were absent. Internally generated waves impinged the sea floor in offshore regions and, because of friction along a wide and shallow sea floor, created a low‐energy expanse of waters across the proximal ramp. Storms were the dominating depositional process capable of disrupting the entire sea floor.  相似文献   

Marine carbonates (recent sedimentary carbonates,I): J. D. Milliman. Springer,Berlin, 1974, 375 pp., DM 66.00     

Noel P. James 《Marine Geology》1976,20(2):176-177

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Aragonite depositional facies in a Late Ordovician calcite sea,Eastern Laurentia     

Noel P. James  Guy M. Narbonne  Alexis K. R. Armstrong 《Sedimentology》2020,67(7):3513-3532

The Black River (Upper Ordovician – Sandbian) and Trenton (Upper Ordovician – Katian) groups are traditionally interpreted as a deepening-upward succession deposited in a progressively subsiding Appalachian Basin margin that contained warm-water, marine, photozoan deposits that pass upward into cool-water, marine, heterozoan carbonates. This succession is customarily interpreted to reflect an incursion of cold, high-latitude ocean waters into the area. This view is herein confirmed for coeval carbonates in the northern part of the basin, particularly the St. Lawrence Platform. They are now well explained in this study on the basis of recent studies of cool-water carbonates and calcite–aragonite seas. Overall the succession is one of Sandbian photozoan ramp deposits succeeded by Katian heterozoan ramp carbonates that changed back to photozoan ramp deposits prior to the Hirnantian glaciation. The current interpretation, that deposition took place throughout a calcite sea time, seems at odds with this series of strata. Instead it is herein proposed that deposition took place during an aragonite sea time wherein calcite sea-like sediments accumulated under cold ocean-water temperatures. Such an interpretation is supported by recent experimental data that supports the importance of seawater temperature on CaCO₃ polymorph precipitation. If correct, this means that some of the evidence for calcite sea deposition through time brought about by global tectonics, should be re-evaluated to make sure it was not simply cool-water carbonate production.  相似文献