Sulfur isotope data and the nature of the hydrothermal systems at the Panguna and Frieda porphyry copper deposits, Papua New Guinea

Abstract Porphyry copper deposits consist of low-grade stockwork and disseminated sulfide zones that contain characteristic vein generations formed during the evolution of the hydrothermal systems. The present contribution examines the influence of variable CO2 concentrations on the solubility of quartz in single-phase hydrothermal fluids forming stockwork veins in porphyry deposits at temperatures of 150° to 550°C and pressures ranging from 100 to 2,000 bar at concentrations up to 8 mol % CO2. The calculations demonstrate that quartz solubility in hydrothermal fluids decreases with increasing CO2 content. Retrograde quartz solubility is less pronounced in CO2-bearing fluids and is not observed in single-phase fluids having CO2 concentrations exceeding 6 mol %. Despite the effects of CO2, retrograde quartz solubility plays an important role in the formation of porphyry stockwork veins that contain little or no quartz as a gangue mineral. At high temperatures and lithostatic pressure conditions below 900 bar, early biotite veins can form as a result of quasi-isobaric cooling of single-phase hydrothermal fluids under conditions of retrograde quartz solubility or near-constant quartz solubility. Stock-work veins consisting of molybdenite or hypogene copper sulfide minerals lacking quartz could form at temperatures of up to 450°C under hydrostatic pressures ranging from ~250 to 900 bar. In the presence of CO2, retrograde quartz solubility is shifted toward slightly lower temperatures at constant pressure. At temperatures below ≾375°C, quartz is precipitated during quasi-isobaric cooling irrespective of CO2 content of the hydrothermal fluids, resulting in the formation of late porphyry quartz veins.

Download Full-text

Ages of Mineralization of Gold and Porphyry Copper Deposits in the New Guinea Highlands

Economic Geology ◽

10.2113/gsecongeo.67.8.1034 ◽

1972 ◽

Vol 67 (8) ◽

pp. 1034-1048 ◽

Cited By ~ 30

Author(s):

R. W. Page ◽

Ian McDougall

Keyword(s):

Porphyry Copper ◽

New Guinea ◽

Porphyry Copper Deposits ◽

Copper Deposits

Download Full-text

INTEGRATED CATHODOLUMINESCENCE AND FLUID INCLUSION STUDIES ON VEIN QUARTZ: UNRAVELING THE EVOLUTION OF MAGMATIC-HYDROTHERMAL SYSTEMS FORMING PORPHYRY COPPER DEPOSITS

10.1130/abs/2016am-284428 ◽

2016 ◽

Author(s):

Thomas Monecke ◽

◽

T. James Reynolds

Keyword(s):

Fluid Inclusion ◽

Porphyry Copper ◽

Hydrothermal Systems ◽

Porphyry Copper Deposits ◽

Vein Quartz ◽

Copper Deposits

Download Full-text

Supergiant porphyry Cu deposits are failed large eruptions

10.21203/rs.3.rs-802055/v1 ◽

2021 ◽

Author(s):

Massimo Chiaradia ◽

Luca Caricchi

Keyword(s):

Porphyry Copper ◽

Volcanic Eruptions ◽

Hydrothermal Systems ◽

Convergent Margins ◽

Porphyry Copper Deposits ◽

Copper Deposits ◽

Porphyry Cu ◽

Shallow Crust ◽

Mass Balance Approach ◽

Injection Rates

Abstract Porphyry copper deposits, the principal natural source of Cu and Mo, form at convergent margins. Copper is precipitated from fluids associated with cooling magmas that have formed in the mantle and evolved at variably deep crustal levels, before raising close to the surface where they exsolve fluids and copper. Despite significant advances in the understanding of their formation, there are still underexplored aspects of the genesis of porphyry copper deposits. Here, we address the role played by magma injection rates into the shallow crust on the formation of porphyry copper deposits with different copper endowments. Using a mass balance approach, we show that supergiant porphyry Cu deposits (>10 Mt Cu) require magma volumes and magma injection rates typical of large volcanic eruptions. Because such volcanic events would destroy magmatic-hydrothermal systems or prevent their formation, the largest porphyry Cu deposits can be considered as failed large eruptions and this may be one of the causes of their rarity.

Download Full-text

A Downgoing Indian Lithosphere Control on Along-Strike Variability of Porphyry Mineralization in the Gangdese Belt of Southern Tibet

Economic Geology ◽

10.5382/econgeo.4768 ◽

2020 ◽

Vol 116 (1) ◽

pp. 29-46 ◽

Cited By ~ 2

Author(s):

Xiang Sun ◽

Yongjun Lu ◽

Qiang Li ◽

Ruyue Li

Keyword(s):

Porphyry Copper ◽

Tectonic Setting ◽

Igneous Rocks ◽

Crustal Thickening ◽

Hf Isotopes ◽

Porphyry Copper Deposits ◽

Bulk Rock ◽

Southern Tibet ◽

Copper Deposits ◽

Isotope Data

Abstract The E-trending Gangdese porphyry copper belt in southern Tibet is a classic example of porphyry mineralization in a continental collision zone. New zircon U-Pb geochronological, zircon Hf-O, and bulk-rock Sr-Nd isotope data for the Miocene mineralizing intrusions from the Qulong, Zhunuo, Jiru, Chongjiang, and Lakange porphyry copper deposits and Eocene igneous rocks from the western Gangdese belt, together with literature data, show that both Paleocene-Eocene igneous rocks and Miocene granitoids exhibit coupled along-arc isotopic variations, characterized by bulk-rock ɛNd(t) and zircon ɛHf(t) values increasing from ~84° to ~92°E and then decreasing toward ~95°E. These are interpreted to reflect increasing contributions of subducted Indian continental materials from ~92° to ~84°E and from ~92° to ~95°E, respectively. The Miocene mineralizing intrusions were derived from subduction-modified Tibetan lower crust represented isotopically by the Paleocene-Eocene intrusions, with contributions from Indian plate-released fluids and mafic melts derived from mantle metasomatized by subducted Indian continental materials. Involvement of isotopically ancient Indian continental materials increased from east (Qulong) to west (Zhunuo), which is interpreted to reflect an increasingly shallower angle of the downgoing Indian slab from east to west, consistent with geophysical imaging. Exploration of Gangdese Miocene porphyry copper deposits should focus on the Paleocene-Eocene arc where the subarc mantle was mainly enriched by fluids from the subducted Neo-Tethyan oceanic slab. Neodymium-Hf isotope data for mineralizing igneous rocks from porphyry copper deposits globally show no obvious correlations with Cu endowment. Although Nd-Hf isotopes are useful for imaging lithospheric architecture through time, caution must be taken when using Nd-Hf isotopes to evaluate the potential endowment of porphyry copper deposits, because other factors such as tectonic setting, crustal thickening, magma differentiation, fluid exsolution, and ore-forming processes all play roles in determining Cu endowments and grades.

Download Full-text