Petrological and Mineralogical Aspects of Epithermal Low-Sulfidation Au- and Porphyry Cu-Style Mineralization, Navilawa Caldera, Fiji

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2019-01-15
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Forsythe, Nathan
Thompson, Michael
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Spry, Paul
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Agronomy

The Department of Agronomy seeks to teach the study of the farm-field, its crops, and its science and management. It originally consisted of three sub-departments to do this: Soils, Farm-Crops, and Agricultural Engineering (which became its own department in 1907). Today, the department teaches crop sciences and breeding, soil sciences, meteorology, agroecology, and biotechnology.

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The Department of Agronomy was formed in 1902. From 1917 to 1935 it was known as the Department of Farm Crops and Soils.

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1902–present

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  • Department of Farm Crops and Soils (1917–1935)

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Geological and Atmospheric Sciences

The Department of Geological and Atmospheric Sciences offers majors in three areas: Geology (traditional, environmental, or hydrogeology, for work as a surveyor or in mineral exploration), Meteorology (studies in global atmosphere, weather technology, and modeling for work as a meteorologist), and Earth Sciences (interdisciplinary mixture of geology, meteorology, and other natural sciences, with option of teacher-licensure).

History
The Department of Geology and Mining was founded in 1898. In 1902 its name changed to the Department of Geology. In 1965 its name changed to the Department of Earth Science. In 1977 its name changed to the Department of Earth Sciences. In 1989 its name changed to the Department of Geological and Atmospheric Sciences.

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1898-present

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  • Department of Geology and Mining (1898-1902)
  • Department of Geology (1902-1965)
  • Department of Earth Science (1965-1977)
  • Department of Earth Sciences (1977-1989)

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Abstract

The Navilawa caldera is the remnant of a shoshonitic volcano on Viti Levu, Fiji, and sits adjacent to the low-sulfidation Tuvatu epithermal Au–Te deposit. The caldera occurs along the Viti Levu lineament, approximately 50 km SW of the Tavua caldera, which hosts the giant low-sulfidation Emperor epithermal Au–Te deposit. Both calderas host alkaline rocks of nearly identical age (~5.4–4.6 Ma) and mineralization that occurred in multiple stages. The gold mineralization in these locations is spatially and genetically related to monzonite intrusions and low-grade porphyry Cu-style mineralization. Potassic, propylitic, phyllic, and argillic alteration extends from the Tuvatu Au–Te deposit towards the central, northern, and eastern parts of the Navilawa caldera where it is spatially associated with low-grade porphyry Cu–Au mineralization at the Kingston prospect and various epithermal Au–(Te) vein systems, including the Banana Creek and Tuvatu North prospects. Chalcopyrite, and minor bornite, occurs in quartz–calcite–(adularia) veins in the Kingston deposit associated with weak propylitic and phyllic alteration, whereas NE-trending epithermal gold veins at the Banana Creek and Tuvatu North prospects are associated with weak potassic alteration that is overprinted by propylitic and phyllic alteration. Gold is accompanied by chalcopyrite, galena, and sphalerite in quartz–pyrite veins that also have a Ag–As–Hg–Te signature. The temperature range for phyllosilicates in the phyllic alteration (chlorite ± smectite ± corrensite ± illite) is in good agreement with temperatures recorded from previous fluid inclusion studies of quartz at the Banana Creek Au prospect (~260 °C) and the nearby Tuvatu Au–Te deposit (205 to 382 °C). Sulfur isotope compositions of pyrite (−6.2 to +0.4‰) from the Banana Creek prospect indicate a likely magmatic source of sulfur. Oxidation of the ore fluids or a direct addition of volatiles to the hydrothermal fluids may account for the lighter isotopic values. The similarities of the igneous rock types and compositions, transition from porphyry- to epithermal-style mineralization, alteration assemblages, paragenetic relationships, and stable isotope data suggest a common origin for the porphyry- and epithermal-style mineralization within the Navilawa and between the Navilawa and Tavua calderas.

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This article is published as Forsythe, Nathan A., Paul G. Spry, and Michael L. Thompson. "Petrological and Mineralogical Aspects of Epithermal Low-Sulfidation Au-and Porphyry Cu-Style Mineralization, Navilawa Caldera, Fiji." Geosciences 9, no. 1 (2019): 42. doi: 10.3390/geosciences9010042.

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Tue Jan 01 00:00:00 UTC 2019
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