Chromite deposits of the north-central Zambales Range, Luzon, Philippines

Rossman, D.L.

doi:10.3133/ofr70281

Cited by 10 publications

(9 citation statements)

References 3 publications

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“…The Zambales Range is composed of an eastward dipping but relatively undeformed block of pillow basalt, gabbro, and perioditc more than 100 km long [Philippine Bureau of Mines, 1963;Rossman, 1964;Hawkins and Evans, 1983; $chweller et al., 1983]. In places, recent and Quaternary volcanic rocks cover the older strata.…”

Section: Regional Geology Of Luzonmentioning

confidence: 99%

“…Gravity models were used to develop structural sections along two east-west multichannel seismic lines across the Manila Trench and fore arc ( This gravity model is consistent with our interpretation that the Zambales ophiolite continues northward offshore of Lingayen Gulf. We interpret the eastward dipping highdensity body to represent the basal ultramafic layers of the Zambales ophiolite, exposed along the coast of western Luzon [Rossman, 1964;Bacuta, 1979 Kelleher, 1976; $eno and Kurita, 1978] suggest that subduction along the Manila Trench may be slowing or has recently ceased. They speculate that such a decrease in the subduction rate might be a response to collisions of Taiwan with Eurasia in the north [Biq, 1971] and portions of Mindoro with southern Luzon [Taylor and Hayes, 1980;1983].…”

Section: And Gravitymentioning

confidence: 99%

See 1 more Smart Citation

A geophysical study of the Manila Trench, Luzon, Philippines: 1. Crustal structure, gravity, and regional tectonic evolution

Hayes¹,

Lewis²

1984

J. Geophys. Res.

159

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The Manila Trench subduction zone is an active convergent plate margin between the South China Sea and the northern Philippines. The trench trends northerly and is associated with a volcanic arc, an east dipping Benioff zone beneath Luzon, and a well‐developed fore arc basin system. The Luzon Trough fore arc basins lie landward of the Manila Trench and contain up to 4.5 km of Cenozoic sediments. Offscraping and accretion of turbidite sediments deposited in the Manila Trench have resulted in the upbuilding and outbuilding of an accretionary prism which forms the seaward margin of the fore arc basin system. The uplifted Zambales ophiolite and its offshore extension form the landward side, of the fore arc basin. Multichannel seismic reflection profiles reveal that folding and thrust faulting of trench strata occur at the base of the trench slope. The major structural décollement at the Manila Trench usually forms near the unconformity separating the hemipelagic sediments from the turbidite sediments. Subduction and perhaps underplating of the basal hemipelagic trench sediments accompany the deformation and accretion of the overlying clastic deposits. Faulting and uplift occur within a narrow zone of the fore arc where seamounts associated with the relict spreading center of the South China Sea basin have presumably been subducted. North of Lingayan Gulf the fore arc is disrupted by active fault systems that trend north and northwest offshore from the Luzon Central Valley and from the southern Cordillera Central. Based on regional geological and tectonic observations, we infer that subduction probably began at the Manila Trench in late Oligocene to middle Miocene time. The long‐term average convergence rate at the Manila Trench is estimated to be between 10 and 20 mm/yr and may be slowing in the north owing to the collision of Taiwan with Eurasia.

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Section: Regional Geology Of Luzonmentioning

confidence: 99%

Section: And Gravitymentioning

confidence: 99%

A geophysical study of the Manila Trench, Luzon, Philippines: 1. Crustal structure, gravity, and regional tectonic evolution

Hayes¹,

Lewis²

1984

J. Geophys. Res.

159

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“…Some chromite bodies occur in dunite layers at the tectonite and cumulate contact (Yigit, 2008). Within the peridotite bodies, chromitite is almost always associated with dunite, troctolite, or serpentine bodies that are near gabbro (Thayer, 1961;Rossman, 1970) or pyroxenite (Wells and others, 1940) and or with chromite-rich channels in dunite in the cumulate layers (Leblanc, 1987;Yigit, 2008). This has led some investigators to conclude that podiform chromite deposits tend to occur at or near (within 1 km) the Moho discontinuity, or transition zone between the overlying cumulate and underlying tectonite zones of ophiolite sequences (Thayer, 1961;Dickey, 1975;Greenbaum, 1977;Engin and others, 1987;Stowe, 1987a;Yigit, 2008).…”

Section: Host Rocks and Structurementioning

confidence: 99%

Podiform chromite deposits--database and grade and tonnage models

Mosier¹,

Singer²,

Moring³

et al. 2012

Scientific Investigations Report

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Chromite ((Mg, Fe++)(Cr, Al, Fe+++) 2 O 4) is the only source for the metallic element chromium, which is used in the metallurgical, chemical, and refractory industries. Podiform chromite deposits are small magmatic chromite bodies formed in the ultramafic section of an ophiolite complex in the oceanic crust. These deposits have been found in midoceanic ridge, offridge, and suprasubduction tectonic settings. Most podiform chromite deposits are found in dunite or peridotite near the contact of the cumulate and tectonite zones in ophiolites. We have identified 1,124 individual podiform chromite deposits, based on a 100-meter spatial rule, and have compiled them in a database. Of these, 619 deposits have been used to create three new grade and tonnage models for podiform chromite deposits. The major podiform chromite model has a median tonnage of 11,000 metric tons and a mean grade of 45 percent Cr 2 O 3. The minor podiform chromite model has a median tonnage of 100 metric tons and a mean grade of 43 percent Cr 2 O 3. The banded podiform chromite model has a median tonnage of 650 metric tons and a mean grade of 42 percent Cr 2 O 3. Observed frequency distributions are also given for grades of rhodium, iridium, ruthenium, palladium, and platinum. In resource assessment applications, both major and minor podiform chromite models may be used for any ophiolite complex regardless of its tectonic setting or ophiolite zone. Expected sizes of undiscovered podiform chromite deposits, with respect to degree of deformation or ore-forming process, may determine which model is appropriate. The banded podiform chromite model may be applicable for ophiolites in both suprasubduction and midoceanic ridge settings.

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“…Clinopyroxene (e.g., Wo,,,En, ,Fs,,) is present only as a minor constituent (<lo%, usually <5%) in some samples from the western part of the unit; these rocks are lherzolites (OL + OPX +CPX). Chromite is an important accessory mineral throughout the unit; it forms ore bodies in the Acoje mine area, and a t several other localities in the block there are chromite claims and inactive chromite mine sites [Rossman, 1964;Bacuta, 19781. The chromite has high Cr/(Cr + Al), low Fe"'lFe", and Mgl (Mg + Fe") of 0.5-0.6 (Table 2). Our data for the minerals, as well as the bulk rock composition, support the interpretation that the unit is derived from a part of the mantle which has been through one or more previous episodes of fractional melting and both a high-T ductile deformation and low-T brittle deformation.…”

Section: Hawkins and Evans 103mentioning

confidence: 99%

“…The ultramafic rocks have great concentrations of both high-Cr and high-A1 chromite [Stoll, 1958;Fernandez, 1960;Rossman, 1964;Bacuta, 1978;Evans and Hawkins, 1980, 19811. Cu-Fe sulfides are mined from blanket-like de~osits interbedded with pillow basalt and basaltic breccia of the ophiolite near Barlo at the north end of the range. Cu-sulfides are also mined in porphyry copper deposits which are in late Tertiary plutons near the north end of the volcanic belt.…”

Section: Introductionmentioning

confidence: 98%

Geology of the Zambales Range, Luzon, Philippine Islands: Ophiolite derived from an island arc-back arc basin pair

Hawkins¹,

Evans²

1983

Geophysical Monograph Series

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The Zambales Range Ophiolite comprises peridotite, gabbro-norite, diabase dikes and sills, and a range of basaltic rock types including pillows, massive and brecciated rocks. The mafic and ultramafic section of the ophiolite is typical of other ophiolites and of rocks presumed to form oceanic crust and upper mantle. The peridotite is mainly saxonite, but extensive areas are underlain by dunite; it has been serpentinized to varied extent throughout all of the range. Chromite is an abundant constituent of the peridotite, and in many areas it forms very large concentrations, some of which are currently being mined. Clinopyroxene is a minor constituent in most of the peridotite mass, but locally there are occurrences of lherzolitic rocks. The entire peridotite mass shows effects of deformation at high temperature (e.g., >600°C) as well as widespread evidence for intense shearing and recrystallization at low temperature (e.g., 200-500°C) with the development of serpentine, talc, and amphibole on fault zones. We recognize two major blocks of crust and upper mantle, Acoje block and Coto block, which are distinguished on the basis of their crustal section thicknesses and on the geochemistry of the crust and mantle rocks. A thick zone (0.7-1.3 km) ofcumulate textured ultramafic rocks with varied amounts of olivine, clinopyroxene, and orthopyroxene structurally overlies the peridotite of the Acoje block. This layered series also contains chromite and sulfide minerals; the layered series grades upward into gabbro-norite and plagioclase is a minor component of layered series rocks near the petrologic contact. The plutonic mafic rocks which overlie the layered ultramafic rocks of the Acoje block are mainly cumulate textured norite. Both massive and layered rocks are present; the layered units of the norite series include anorthosite, pyroxenite, olivine norite, and a wide range of norite varieties having variable proportions of the major minerals. Calcic amphibole is a minor late magmatic mineral. The upper levels of the Acoje block norite have quartz-rich norite and hypersthene quartz diorite layers and intrusive masses. An upper norite phase merges with massive and tabular (sill-dike) diabase and with a tonalite-trondhjemite series. The Coto block lacks the layered ultramafic series, and the mafic units are mainly gabbro. The Coto-layered gabbros include gabbroic anorthosite, pyroxenite, olivine gabbro, troctolite, allivalite, and some layers which are nearly anorthosite in compositions. Cumulate textures and both rhythmic and cryptic layering are present. Hypersthene is a very rare component of this series except as a reaction rim on olivine. Diabase and basaltic rocks structurally overlie both the norite and gabbro series. In many areas, such as on the Camiling and Moriones Rivers of the Coto block and on the Sual coast of the Acoje block, there are structural-textural gradations from plutonic to hypabyssal rocks. A similar gradation from the diabase sills-dikes to pillow basalts is well shown on the Camiling River, the N...

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Chromite deposits of the north-central Zambales Range, Luzon, Philippines

Cited by 10 publications

References 3 publications

A geophysical study of the Manila Trench, Luzon, Philippines: 1. Crustal structure, gravity, and regional tectonic evolution

A geophysical study of the Manila Trench, Luzon, Philippines: 1. Crustal structure, gravity, and regional tectonic evolution

Podiform chromite deposits--database and grade and tonnage models

Geology of the Zambales Range, Luzon, Philippine Islands: Ophiolite derived from an island arc-back arc basin pair

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