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.
Highlights
A spatial and genetic relationship exists between low-sulfidation gold deposits and alkaline igneous rocks [1,2,3], especially in the southwest Pacific in the Acupan, [4], Porgera, [5,6], Mt
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
A preliminary study of the alteration assemblages was previously made at the Tuvatu [11] deposit, the current study has focused on the different types of alteration in the Banana Creek and Tuvatu North prospects
Summary
A spatial and genetic relationship exists between low-sulfidation gold deposits and alkaline igneous rocks [1,2,3], especially in the southwest Pacific in the Acupan, [4], Porgera, [5,6], Mt. A regional gravity survey shows strong bullseye gravity anomalies >20 km in diameter that correlate with the position of four volcanic calderas in the northwestern part of the island of Viti Levu, Fiji: Tavua, Rakiraki, Ba, and Navilawa [15,16]. Each of these calderas is spatially associated with epithermal gold mineralization and occurs along the prominent regional Viti Levu lineament [17]. The Tuvatu Au–Te deposit, which occurs approximately 50 km southeast of Emperor, is one of several epithermal gold telluride and low-grade porphyry Cu prospects that occur in or on the margins of the Navilawa caldera [17]
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