Alternating chert-clastic sequences juxtaposed with limestone blocks, which are

No abstract

Northwest Panay consists of two terranes that form part of the Central Philippine collision zone: Buruanga Peninsula and Antique Range. The Buruanga Peninsula consists of a Jurassic chert-clastic-limestone sequence, typical of oceanic plate stratigraphy of the Palawan Micro-continental Block. The Antique Range is characterized by Antique Ophiolite Complex peridotites and Miocene volcanic and clastic rocks, representing obducted oceanic crust that serves as the oceanic leading edge of the collision with the Philippine Mobile Belt. The Nabas Fault is identified as the boundary between the two terranes. This study employed the gravity method to characterize the Northwest Panay subsurface structure. Results indicate higher Bouguer anomaly values for Buruanga Peninsula than those for Antique Range, separated by a sudden decrease in gravity values toward the east-southeast (ESE) direction. Forward gravity data modeling indicates the presence of an underlying basaltic subducted slab in the Buruanga Peninsula. Furthermore, the Nabas Fault is characterized as an east-dipping thrust structure formed by Buruanga Peninsula basement leading edge subduction beneath Antique Range. Additional geophysical constraints were provided by shallow seismic refraction and electrical resistivity surveys. Results from both methods delineated the shallow subsurface signature of the Nabas Fault buried beneath alluvium deposits. The gravity, seismic refraction and electrical resistivity methods were consistent in identifying the Nabas Fault as the terrane boundary between the Buruanga Peninsula and the Antique Range. The three geophysical methods helped constrain the subsurface configuration in Northwest Panay.

The Rorah Kadal vein is located in the Cibaliung goldfield, Western Java, Indonesia. The vein is hosted by the Miocene Honje Igneous Complex and composed of sequences of basalt-andesite lava flows, volcanic breccia, and overlain by tuff. The paper is tending to describe occurrence, alteration, mineralogy, and fluid inclusion microthermometry of the Rorah Kadal gold-bearing quartz vein to understand the process and formation condition of gold mineralization. The Rorah Kadal is a single vein trending NW direction and about 700 meters parallel to main Cibaliung vein. The alteration consists of illite/smectite mixed layer mineral-adularia-quartz, chlorite-chlorite/smectite mixed layer mineral, and illite-illite/smectite mixed layer mineral-calcite-quartz zones. The vein types are colloform-crustiform band, breccia, vug, cockade, and comb, which are mainly composed of quartz and adularia. Based on quartz textures, three stages of mineralization are recognized: Stage-1 colloform-crustiform; Stage-2 hydrothermal breccia; and Stage 3- late stage quartz veinlet textures. The ore mineralogy of the Rorah Kadal quartz vein is mainly pyrite, chalcopyrite, galena, sphalerite, electrum, and aguilarite. Fluid inclusion temperatures from five drill core quartz samples ranges from 180 to 330 °C, with salinities varying from 1.2 to 4.0 wt% NaCl. The Rorah Kadal vein has slightly high fluid temperature and salinity as compared to Cikoneng and Cibitung veins of the Cibaliung goldfield. This data suggests that the hydrothermal fluids appear to have formed from low temperature and low salinity fluids in near neutral pH environment.