Rota Island, the southernmost island in the Commonwealth of the Northern Mariana Islands in the western Pacific, has the types of caves previously documented on the other limestone mantled islands in the Mariana Arc that have been investigated for caves: Aguijan, Guam, Tinian and Saipan. Caves developed at the edge of the fresh-water lens by zones of enhanced carbonate dissolution produced by fresh-water/salt-water mixing are most common. Among these mixing zone caves, flank margin caves dominate. Flank margin caves were found singly and in extensive horizons representing significant sea-level still stands. However, another type of mixing zone cave was found on Rota in numbers not documented on neighboring islands. Mixing zone fracture caves, apparently formed as zones of enhanced dissolution, produced fresh-water discharging from the lens along fractures, migrated vertically as sea-level changed. Some mixing zone fracture caves on Rota are developed in clusters from two to four caves. The mixing zone caves of Rota reflect the interaction of eogenetic limestone, glacioeustasy, local tectonics and enhanced carbonate dissolution via mixing of disparate waters. The development of mixing zone caves on Rota is in agreement with the Carbonate Island Karst Model (CIKM). Rota has a few caves developed along the contact between limestone and the insoluble volcanic rock that makes up the core of the island. The most important of these is Water Cave, a large spring that is the source for most of the municipal water on Rota. Rota also two extensive zones of vertical fissures developed along bedrock fractures; Fissure City and As Mundo Fissure Zone. In addition, Rota has one cave apparently developed along a fault; Gagani Cave. Some of the caves documented on Rota are difficult to classify and warrant further investigation.

Abaco Island is located on Little Bahama Bank at the northwestern extent of the Bahamian Archipelago. Karst features on Abaco include: flank margin caves, karren, blue holes, pit caves, banana holes, and cone karst. As part of this study all known flank margin caves on Abaco were GPS located and surveyed. The presence and locations of the other karst features were recorded as part of the karst inventory of Abaco. The cone karst is of particular interest because cone karst has not been documented on other Bahamian islands. These cones form from the dissection of an eolianite ridge due to karst, fire, and vegetative processes. Tafoni-like recesses, originally believed to be high flank margin caves, were formed during cliffing of an eolianite ridge during the OIS 5e highstand. The geologic evolution of representative depositional sequences on Abaco fits within the accepted Bahamian stratigraphy.

Mississippi Valley Type (MVT) lead and zinc deposits provide a significant source of sedimentary galena and sphalerite. However, geochemical characteristics and genesis including the source and production of hydrogen sulfide required for galena and sphalerite ore formation and the reasoning for quick, episodic mineralization is not fully understood. By simulating regional MVT brines, the input and effect of biological by-products during the development of these ores as well as the cause of cyclicity within MVT deposits have been observed. Experiments using compositions from MVT fluid inclusions were conducted over two-week periods. Variables during the experiments included temperature, CO2, hydrogen sulfide (H2S), lead and zinc. Removal of H2S at 70 oC caused no sulfide precipitation. Conclusions of this study are that fluid mixing or in-situ sulfur reduction by thermochemical or biogenic means are the primary mechanisms of MVT deposition, while at low temperatures biogenic sulfur reduction is the main driver.

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