Vishiti, Akumbom, Petersen, Sven , Suh, C. E. and Devey, Colin W. (2014) Texture, mineralogy and geochemistry of hydrothermally altered submarine volcanics recovered southeast of Cheshire Seamount, western Woodlark Basin. Marine Geology, 347 . pp. 69-84. DOI 10.1016/j.margeo.2013.11.002.

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Abstract

The western Woodlark Basin lies within a gold-rich metallogenic province. This area is characterized by detachment
faults that record ongoing extension and act as major pathways for the circulation of hydrothermal fluids.
Dredging from the flanks of a submarine ridge southeast of Cheshire Seamount, western Woodlark Basin retrieved
hydrothermally altered monomictic to polymictic crackle, mosaic and chaotic breccias with at least 30%
clasts N2 mmin diameter. The precursor rocks are andesitic to rhyolitic in composition, but have been intensely
hydrothermally altered, with about 90% of the volcanic glass replaced by secondaryminerals. The breccias show
five generations of quartz growth, with the first being related to magmatic processes and the remaining four to
alteration stages including silicification, chloritization, illitization, sericitization, albitization, and sulfidation.
Needle-like crystals ofmordenite (zeolite)withmultiple growth centers growon the fourth generation of quartz.
Notable textural variants in the breccias are vesicles, perlitic cracks, and zoned alteration halos that mantle the
rims of clasts. Electron microprobe analyses on chlorite from breccia samples have identified clinochlore as the
main chlorite type and indicate a formation temperature in the range of 210–304 °C. This and the elevated
Au–As–Ag–Hg–Zn–Pb–Sb contents of a mineralized sample indicate hydrothermal alteration temperatures
N200 °C suggesting that these breccias may represent the upflow zone of a hydrothermal system and highlight
the potential for seafloor massive sulfides in the area. The breccias show elevated contents of immobile trace
elements and LREE as well as a depletion in Ta and Nb suggesting that the precursor rocks were formed in a
rift-related suprasubduction environment.

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