Geochronology of the Porgera gold deposit, Papua New Guinea: Resolving the effects of excess argon on K-Ar and sup 40 Ar/ sup 39 Ar age estimates for magmatism and mineralization

Journal Article · Tue May 01 00:00:00 EDT 1990 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(90)90164-G· OSTI ID:6243855

Richards, J P; McDougall, I ^[1]

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1. Australian National Univ., Canberra (Australia)

Mesothermal/epithermal gold mineralization at Porgera in the highlands of Papua New Guinea (PNG), occurs in structurally controlled veins and disseminations, which overprint and cross-cut a suite of shallow-level, comagmatic, mafic alkaline stocks and dykes and their sedimentary host rocks. Conventional K-Ar apparent ages of twelve hornblende separates from eight different intrusions scatter between 7 and 14 Ma, but four biotite separates are concordant at 6.02 {plus minus} 0.29 Ma (2{sigma}). {sup 40}Ar/{sup 39}Ar step-heating experiments on six of the hornblende separates reveal saddle-shaped age spectra, which indicate the presence of excess {sup 40}Ar. One of these samples yields a well-defined plateau with an apparent age of 5.96 {plus minus} 0.25 Ma (2{sigma}). Conventional K-Ar analyses of six separates of hydrothermal illite and roscoelite associated with gold mineralization yield apparent ages of between 5.1 and 6.1 Ma and indicate that ore deposition occurred within 1 Ma of magmatism at Porgera. Evidence for the evolution of a magmatic volatile phase, and the presence of excess {sup 40}Ar both in the intrusives and in hydrothermal fluids associated with the orebody, suggest that magmatic fluids may have had some involvement in metallogenesis, but the exact nature of this involvement is not yet clear. Late Miocene magmatism and mineralization at Porgera are thought to have occurred shortly prior to or during the initiation of continent/arc collision and to pre-date associated Pliocene uplift and foreland deformation in the highlands.

• OSTI ID: 6243855
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 54:5; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GOLD ORES
MINERALIZATION
ROCK-FLUID INTERACTIONS
PLUTONIC ROCKS
ISOTOPE DATING
PETROGENESIS
ARGON 39
ARGON 40
BIOTITE
GEOLOGIC HISTORY
HORNBLENDE
HYDROTHERMAL ALTERATION
MAGMATISM
MIOCENE EPOCH
PAPUA NEW GUINEA
POTASSIUM ISOTOPES
AGE ESTIMATION
ALKALI METAL ISOTOPES
AMPHIBOLE
ARGON ISOTOPES
ASIA
AUSTRALASIA
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CENOZOIC ERA
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC AGES
IGNEOUS ROCKS
ISLANDS
ISOTOPES
LIGHT NUCLEI
MICA
MINERALS
NEW GUINEA
NUCLEI
ORES
RADIOISOTOPES
ROCKS
SILICATE MINERALS
STABLE ISOTOPES
TERTIARY PERIOD
YEARS LIVING RADIOISOTOPES
580000* - Geosciences