Elemental Gains and Losses during Hydrothermal Alteration in Awak Mas Gold Deposit, Sulawesi Island, Indonesia: Constraints from Balanced Mineral Reactions

Hydrothermal gold mineralization is commonly associated with metasomatic processes resulting from interaction of hostrock with infiltrating hot aqueous fluids. Understanding of the alteration mechanism requires quantification of element changes in altered rock, relative to the unaltered or least-altered rock, representing the protolith. Balanced mineral reactions are used to gain quantitative insight into the alteration process associated with gold mineralization at the Awak Mas deposit. Three representative samples were carefully selected from the least-altered pyllite and the two alteration zones bordering the mineralization. Mineral mode, textural features, and mineral compositions were studied by microscopy and electron microprobe analyzer (EMPA). Quantitative modal analysis was performed with a Quanta 650 F QEMSCAN® system. The hydrothermal alteration sequence around the mineralization starts with the proximal albite–ankerite–pyrite alteration zone via the distal albite–chlorite alteration zone to the least-altered phyllite wall-rock. Balanced mineral reaction calculations were performed to evaluate elemental gains and losses. Most noticeable is the addition of Si, Na and Ca to each alteration zone. This alteration is represented by the almost complete replacement of muscovite by albite. The addition of Fe and S was highest in the albite–ankerite–pyrite alteration zone. Alteration of the least altered phyllite to the albite–chlorite zone involved a mass increase of 14.5% and a neglectable volume increase of 0.6%. The mass and a volume increase from the least altered phyllite to the albite–ankerite–pyrite zone was 40.5% and 0.47%, respectively. The very low volume change during alteration is also corroborated by the textural preservation indicating isovolumetric metasomatic reactions. The replacement of muscovite by albite may have had an important effect on the change of the rock failure mode from ductile to brittle, with consequences for the focusing of fluid flow.

[1]  L. Lobato,et al.  Hydrothermal alteration and mineralization in the Faina greenstone belt: evidence from the Cascavel and Sertão orogenic gold deposits , 2020 .

[2]  F. Meyer,et al.  Hydrothermal alteration and gold mineralization of the Awak Mas metasedimentary rock-hosted gold deposit, Sulawesi, Indonesia , 2019, Ore Geology Reviews.

[3]  B. Zoheir,et al.  Ediacaran (~ 600 Ma) orogenic gold in Egypt: age of the Atalla gold mineralization and its geological significance , 2019 .

[4]  R. Takahashi,et al.  Geological and Geochemical Characteristics of Gold Mineralization in the Salu Bulo Prospect, Sulawesi, Indonesia , 2018, Resource Geology.

[5]  W. Prochaska,et al.  Formation of epizonal gold mineralization within the Latimojong Metamorphic Complex, Sulawesi, Indonesia: Evidence from mineralogy, fluid inclusions and Raman spectroscopy , 2018, Ore Geology Reviews.

[6]  Thomas Cudahy,et al.  White mica as a hyperspectral tool in exploration for the sunrise dam and Kanowna belle gold deposits, Western Australia , 2017 .

[7]  R. Hall,et al.  The geological history of the Latimojong region of western Sulawesi, Indonesia , 2017 .

[8]  R. Hall,et al.  Basement character and basin formation in Gorontalo Bay, Sulawesi, Indonesia: new observations from the Togian Islands , 2011 .

[9]  R. Powell,et al.  Formation of gold deposits: a metamorphic devolatilization model , 2010 .

[10]  F. Meyer,et al.  Mineralogy, Lithogeochemistry and Elemental Mass Balance of the Hydrothermal Alteration Associated with the Gold‐rich Batu Hijau Porphyry Copper Deposit, Sumbawa Island, Indonesia , 2009 .

[11]  D. Craw,et al.  Hydrothermal alteration styles in ancient and modern orogenic gold deposits, New Zealand , 2009 .

[12]  F. Meyer,et al.  Balanced mineral reactions for alteration zones developed in auriferous shear zones of the Hutti Mine, Dharwar Craton, India , 2008 .

[13]  T. V. Leeuwen,et al.  Petrologic, isotopic, and radiometric age constraints on the origin and tectonic history of the Malino Metamorphic Complex, NW Sulawesi, Indonesia , 2007 .

[14]  A. Stefánsson,et al.  Gold(I) complexing in aqueous sulphide solutions to 500°C at 500 bar , 2004 .

[15]  F. Bierlein,et al.  Lithogeochemistry of orogenic gold deposits in Victoria, SE Australia: a preliminary assessment for undercover exploration , 2004 .

[16]  Alan R. Butcher,et al.  Rapid quantitative mineral and phase analysis using automated scanning electron microscopy (QemSCAN); potential applications in forensic geoscience , 2004, Geological Society, London, Special Publications.

[17]  A. Stefánsson,et al.  Stability of chloridogold(I) complexes in aqueous solutions from 300 to 600°C and from 500 to 1800 bar , 2003 .

[18]  T. V. Leeuwen,et al.  Spatial and temporal isotopic domains of contrasting igneous suites in Western and Northern Sulawesi, Indonesia , 2003 .

[19]  P. Gottlieb,et al.  Using quantitative electron microscopy for process mineralogy applications , 2000 .

[20]  R. Kretz.  REDISTRIBUTION OF MAJOR AND TRACE ELEMENTS DURING THE FORMATION OF BIOTITE–PLAGIOCLASE REACTION ZONES AT BOUNDARIES BETWEEN AMPHIBOLITE AND K-FELDSPAR GNEISS, OTTER LAKE AREA, QUEBEC, CANADA , 2000 .

[21]  T. McCuaig,et al.  P—T—t—deformation—fluid characteristics of lode gold deposits: evidence from alteration systematics , 1998 .

[22]  E. Mikucki.  Hydrothermal transport and depositional processes in Archean lode-gold systems: A review , 1998 .

[23]  C. Parkinson.  An outline of the petrology, structure and age of the Pompangeo Schist Complex of central Sulawesi, Indonesia , 1998 .

[24]  H. Taylor.  Oxygen and hydrogen isotope relationships in hydrothermal mineral deposits , 1997 .

[25]  A. Williams-Jones,et al.  Mass transfer and the path of metasomatic reactions in mesothermal gold deposits; an example from Flambeau Lake, Ontario , 1996 .

[26]  G. Albino.  Sodium metasomatism along the Melones Fault Zone, Sierra Nevada Foothills, California, USA , 1995, Mineralogical Magazine.

[27]  L. Baumgartner,et al.  A least-squares approach to mass transport calculations using the isocon method , 1995 .

[28]  J. Ferry,et al.  Metasomatism and fluid flow in ductile fault zones , 1992 .

[29]  J. Selverstone,et al.  Fluid channelling during ductile shearing: transformation of granodiorite into aluminous schist in the Tauern Window, Eastern Alps , 1991 .

[30]  J. Bohlke.  Comparison of metasomatic reactions between a common CO 2 -rich vein fluid and diverse wall rocks; intensive variables, mass transfers, and Au mineralization at Alleghany, California , 1989 .

[31]  J. A. Grant.  The isocon diagram; a simple solution to Gresens' equation for metasomatic alteration , 1986 .

[32]  J. Boehlke,et al.  Rb-Sr, K-Ar, and Stable Isotope Evidence for the Ages and Sources of Fluid Components of Gold-Bearing Quartz Veins in the Northern Sierra Nevada Foothills Metamorphic Belt, California , 1986 .

[33]  D. Groves,et al.  The nature, genesis and regional controls of gold mineralization in Archaean greenstone belts of the Western Australian Shield; a brief review , 1985 .

[34]  G. N. Phillips,et al.  The nature of Archaean gold‐bearing fluids as deduced from gold deposits of Western Australia , 1983 .

[35]  R. Coveney.  Gold quartz veins and auriferous granite at the Oriental Mine, Alleghany District, California , 1981 .

[36]  E. Essene,et al.  Evaluation of Coexisting Garnet-Biotite, Garnet-Clinopyroxene, and Other Mg-Fe Exchange Thermometers in Adirondack Granulites , 1980 .

[37]  W. Fyfe,et al.  Local modification of rock chemistry by deformation , 1977 .

[38]  R. L. Gresens.  Composition-volume relationships of metasomatism , 1967 .