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R. R. Carlson

Publications and source records attributed to R. R. Carlson.

14 recordsLinked to original sources
USGS1992

Placer and lode platinum-group minerals in south Kalimantan, Indonesia: Evidence for derivation from Alaskan-type ultramafic intrusions

Platinum‐group element minerals (PGM) occur in significant proportions in placer deposits in several localities in South Kalimantan. They consist of Pt‐Fe alloy that may be intergrown with or contain inclusions of Ir‐Os‐Ru alloy, laurite and chromite. Alluvial PGM found along Sungai Tambanio are in part derived from chromitite schlieren in dunitic bodies intruded into clinopyroxene cumulates that may be part of an Alaskan‐type ultramafic complex. A chromitite schlieren in serpentinite from one of these dunitic bodies is anomalous in PGE (Pt: 580 ppb; Pd: 3.4 ppb; Rh: 1 ppb; Ru: 9 ppb; Ir: 21 ppb; and Os: 3.9 ppb). The chondrite‐normalized PGE pattern for this rock, pan concentrates from this area, and PGM concentrates from diamond‐Au‐PGM placer deposits have an ‘M'‐shaped pattern enriched in Ir and Pt that is typical of PGE‐mineralization associated with Alaskan‐type ultramafic complexes.

South Kalimantan↗
USGS1986

Platinum-group element geochemistry of zoned ultramafic intrusive suites, Klamath Mountains, California and Oregon

Three postorogenic Alaskan-type ultramafic to mafic intrusive suites in the Klamath Mountains, ranging in age from 142 to 163 m.y. and intruding metavolcanic, metasedimentary, or ophiolitic cumulate ultramafie to gabbroic rocks, were examined for their platinum-group element content. The Lower Coon Mountain pluton consists of layered clinopyroxene-rich lithologies occurring in chronological sequence whereas the intrusive suite at Tincup Peak consists of a cogenetic sequence of wehrlite, clinopyroxenite, magnetite clinopyroxenite, feldspathic hornblende-magnetite clinopyroxenite, dunite-olivine clinopyroxenite, and hornblende gabbro. The ultramarie-mafic intrusive suite at Chanchelulla Peak, part of the Wildwood pluton, consists predominantly of clinopyroxenite, minor interlayered dunite, and wehrlite with minor hypabyssal gabbroic rocks. Clinopyroxene compositions in the three intrusive suites are calcium rich and range from Wo (sub 54.7) -En (sub 45.1) -Fs 19 to Wo (sub 44.9) -En (sub 43.8) -Fs (sub 11.3) and resemble clinopyroxene with alkalic affinities. Olivine ranges from Fo 72 to Fo 83 and plagioclase from An 68 to An 96 . Cyclic units of layered cumulus magnetite + spinel (+ or -ilmenite) and coarse interstitial magnetite occur at Tincup Peak and Lower Coon Mountain. All three intrusive suites contain disseminated pyrrhotite + chalcopyrite + or - pentlandite, but the Chanchelulla Peak intrusive body also contains lenticular zones of disseminated to interstitial sulfides near its contact with sulfide-bearing horn-felsic rocks. Characteristics of rocks from these three Klamath Mountains Alaskan-type intrusive suites are (1) Rh contents of near or less than 1 ppb, (2) Ir and Ru contents less than 100 and 20 ppb, (3) variable Pd contents between rock units within intrusive suites and among suites, and (4) relatively similar Pt contents within intrusive suites and among suites. Concentrations of Pd average 6.3 ppb at Lower Coon Mountain, 13.7 ppb at Chanchelulla Peak, and 36.4 ppb at Tincup Peak. Cohen-corrected abundance data for individual rock units within each intrusive suite yield a Pt/(Pt + Pd) ratio that is greater in olivine-rich rocks than in clinopy-roxenite than in gabbro suggesting chemical fractionation of Pd within intrusive suites.

Economic Geology↗