Powered by
Teklogin
copyright 2004©
www.prlsamp.org
|
Geosciences |
CHARDÓN, SAMANTA; Ramírez, Wilson R., Prof., UPR-MAYAGÜEZ, Arts & Science, Department of Geology
Water Chemistry in Mona Island and its implications on rock-water interactions
Mona Island is located approximately half way between Puerto Rico and Hispaniola. Due to its isolation and mineralogical composition, the island offers an unique laboratory to study the chemical and physical behavior of groundwater as well as rock-water interactions in an isolated carbonate island. The chemistry of the groundwater was characterized by sampling waters from springs, caves, and wells. Sr isotopic compositions (87Sr/86Sr) were also obtained trying to understand rock-water interactions and influences in the development of dolomites, aquifers, caves, and karst features. In the aquifers, specific conductance, pH, alkalinity, pCO2 , and salinity suggested diagenetic environments produced by the mixing of fresh and marine waters. Over saturaturation with respect to calcite, aragonite, and dolomite, is present in the aquifers. This does not imply that dolomitization is happening, but suggests that these environments are more suitable for dolomitization. Calculations using the dolomitic (González, 1997) and cave dripping water (this study) strontium isotope concentrations suggested that dolomitization may have occurred in Mona as early as the early Miocene. Multiple lines of geochemical and geologic evidence will help to determine the timing of dolomitization and develop a model for dolomitization and cave formation for Mona island.
DEL CORO, MÓNICA; Ramírez, Wilson R., Prof., UPR-MAYAGÜEZ, Arts & Science, Department of Geology
Dolomitization in the Aymamón Limestone (Miocene) of Northern Puerto Rico
The Aymamón Limestone forms an unconfined aquifer system in the Puerto Rico North Coast. Dolomite is abundant in the unit but decreases with stratigraphic depth. Skeletal components, micrite cements, and matrix are dolomitic. Red Algae and Rhodolite facies are pervasively dolomitic. Dolomitization was preceded by early marine cementation, dissolution and/or neomorphism of calcitic and aragonitic components, and infilling of skeletal and intraskeletal porosity by equant/blocky calcite spar. After dolomitization infilling of skeletal and intraskeletal porosity by equant/blocky calcite spar continued.
The dolomites are calcian with CaCO3 mean mole percentage of 53. Average d 18O and d 13C values relative to PDB are +3.7 0/00 (+ 0.9 0/00) and +2.0 0/00 (+ 0.8 0/00) respectively. Mean dolomitic Sr concentration is 243 ppm. Fe and Mn mean concentrations in the dolomites are 4,183 ppm and 100 ppm respectively. These petrographical and geochemical data suggest dolomitization by a mixture of marine and aquifer waters. Sr isotopic ratios are bimodal in distribution. Surface samples ratios are higher (0.709018 + 0.000008) than subsurface ratios (0.708965 + 0.000008). If effected by marine waters these Sr isotopic ratios would suggest two different times of dolomitization, middle and late Miocene. However, these variations can be explained also by Sr contamination from non-marine waters. Dolomites with higher 87Sr/86Sr ratios provide a better estimate of the time of dolomitization since petrography suggest late dolomitization. Dolomitization probably occurred during the late Miocene.
FONG, YOLANDA; Schellekens, Johannes, Prof., UPR-MAYAGÜEZ , Arts & Science, Department of Geology
Erosion of Sediments Resulting from Mineral Exploration in the Pellejas Watershed, Adjuntas, Puerto Rico
In the late 1950’s mineral explorations lead to the discovery of several porphyry copper deposits, amongst other Sapo Alegre, Piedra Hueca and Cala Abajo deposits near Adjuntas, Puerto Rico. Subsequent drilling established that the Piedra Hueca and Cala Abajo deposits were probably economic and several permits were requested, but were never given.
The main objective of this research was to determine the type and the quantity of sediments lost by run off from the vegetated and non-vegetated areas in the mineral exploration site.
Wet Sieving, Sedigraph Particle Size Analysis and X-Ray Diffractometer analysis was carried out to accomplish these objectives. Most of the sediment was trapped in the non-vegetated areas, indicating that here was more erosive and thus that vegetation plays an important role in “holding” the soil. Grain size analysis reveal a tendency of the sediments from lower elevation to be well sorted whereas the ones form higher elevations tend to be poorly sorted. The XRD reveals that the most abundant minerals found were quartz and clay minerals and that the concentration of copper in the area seems to be not significant. A possible explanation is that the copper minerals are soluble and are dissolved in water and consequently carried away.
RIVERA RIVERA, GARYMAR; Schellekens, Johannes, Prof.; Gilbes, Fernando, UPR-MAYAGÜEZ, Arts & Science, Department of Geology; Ysa, Yuri, UPR-MAYAGÜEZ, Department of Computer Engineering
Remote Sensing of Metal Enriched Areas in Tropical Terrains - Porphyry Copper Deposits in West-Central Puerto Rico
At least eight porphyry copper type mineral deposits are described in west central Puerto Rico. These deposits occur associated with small stocks (300 to 1000 m diameter) of tonalite and quartz diorite porphyry of Eocene age, and are characterized by hydrothermal alteration. The soils on top of the porphyry copper deposit and its aureole contain anomalies of metals, with the Cu and Au predominantly over the deposit and the Zn and Pb over the aureole. These methods are not suited for tropical terranes because the usually dense vegetation hiding rocks from remote sensors. However the metal content in the soil may affect the type of vegetation and a distinct shift in the spectral position of chlorophyll bands was distinguished in forests affected by metal-induced stress only in temperate zones (Collins et al., 1983; Chang & Collins, 1983).
The belt containing the porphyry copper deposits, characterized by the extensive envelop of hydrothermally altered rock, allows the study of the environmental effects of mineral deposits using satellite images. The belt includes both economic porphyry copper deposits, as well as low-grade uneconomic and unmineralized intrusive bodies. In a first step, reflectance spectra from native plant species growing on and away from the deposits will be determined by the interpretation of airborne multispectral scanner (MSS) data. Leaves of the top of the canopy are sampled and analyzed using a LICOR integrating sphere attached to the GER 1500 spectroradiometer in order to determine the reflectance spectra of the native tropical vegetation and look for distinguishing spectra.