Geology Reports⌕ Search

Geology topics

Research about Puerto Rico

Source-linked reports with geographic coverage including Puerto Rico.

At least 343 records · Page 19Linked to original sources
USGS1976

History of dredging and filling of lagoons in the San Juan area, Puerto Rico

Laguna La Torrecilla, Laguna de Pinones, Laguna San Jose, and Laguna del Condado, in the San Juan, Puerto Rico area, are located within a metropolitan area of more than 1 million people. Bathymetric maps made during the study, in 1973, showed that Lagunas La Torrecilla, San Jose, and del Condado have been modified by dredging and filling; whereas, Laguna de Pinones has remained in a near natural state. Laguna La Torrecilla has been dredged to a depth, in places, of about 18 meters, and Lagunas San Jose and del Condado, in places to about 11 meters. Dredging in the San Juan lagoons has been harmful, beneficial, and in a few instances has had little or no noticeable effect on the water quality. Usually, dredging in the connecting canals has been beneficial if the water entering the lagoons through the canals was of better quality than the water in the lagoon. Dredging in the mouths of lagoons has been beneficial; whereas, filling or blocking the mouths has been harmful.

Puerto Rico↗
USGS1976

The source of hydrothermal solutions at Puerto Maunabo and its bearing on the base-metal-potassium feldspar association in Puerto Rico

A quartz oligoclase porphyry exposed near Puerto Maunabo may provide evidence to further our understanding of the base-metal-potassium feldspar association known to occur in many of the porphyry-type copper deposits of Puerto Rico. The porphyry appears to be a magmatic differentiate on the border of the San Lorenzo batholith that may represent a source of mineralizing hydrothermal solutions. The porphyry intrudes an albitized quartz diorite border phase of the batholith that contains large roof pendants of metavolcanic rock. These roof pendants are mostly metamorphosed to greenschist metamorphic facies, but in the vicinity of Puerto Maunabo south of the porphyry, they reach amphibolite metamorphic facies; north of the porphyry, similar xenolithic lenses of metavolcanic rock appear to have been converted entirely to an oligoclase quartz felsite. The layered albitized quartz felsite has the same composition and texture as irregular veinlets in the albitized quartz diorite and as the groundmass in the porphyry. The K + ions arid basic ions of Fe +2 , Cu +2 , Mg +2 apparently were mobilized during final magmatic crystallization and then escaped as hydrothermal solutions that followed open conduits within a zone of structural weakness which also permitted the emplacement of the porphyry. The volcanic rock of Cerro Piedra Hueca, in contact with the albitized quartz diorite, and generally along strike west of the porphyry, has been altered to a quartz sericite rock entirely devoid of mafic silicates. This is the southeasternmost exposure of hydrothermally altered volcanic rock in the regional zone of northwest-trending faults that contains the principal porphyry-type copper deposits of Puerto Rico. The texture, mineralogy, and geologic environment of the porphyry at Puerto Maunabo are similar to those of the ore-bearing porphyries but differ in one important aspect. Most ore-bearing porphyries contain hydrothermal potassium feldspar and reddish-brown biotite intimately associated with the base-metal sulfides. In the porphyry of Puerto Maunabo, potassium feldspar is conspicuously absent, and only a trace of biotite is present; the only sulfide present is pyrite. The physical and chemical environment required to precipitate K + ions, either as potassium feldspar or biotite, apparently is very similar to that required to precipitate base-metal sulfides. At Puerto Maunabo, these conditions evidently did not prevail, and potassium and the base metals may have been carried in solution to a more favorable environment.

Puerto Maunabo↗
USGS1975

Geology, geochemistry, and fluid-inclusion petrography of the Sapo Alegre porphyry copper prospect and its metavolcanic wallrocks, west-central Puerto Rico

The Sapo Alegre prospect, a small porphyry copper-molybdenum occurrence in west-central Puerto Rico, is characterized by distinct zones of alteration and mineralization of quartz diorite porphyry. A biotite-chlorite zone in the porphyry near its contact with surrounding metavolcanic rocks contains copper, molybdenum, gold, silver, selenium, and tellurium. A quartz-sericite-pyrite zone within the porphyry contains abundant sulfur and traces of selenium, but metals of the biotite-chlorite zone are nearly absent and zinc, manganese, nickel, sodium, calcium, and magnesium contents are very low. Quartz grains in the biotite-chlorite zone contain abundant fluid inclusions in which halite crystals are common, whereas in the quartz-sericite-pyrite zone inclusions are less abundant and rarely contain halite inclusions. Metavolcanic rocks northwest of the mineralized porphyry are altered to amphibolitic hornfels near the contact. Biotitic alteration is strong outward from the hornfels and grades into chlorite alteration. The hornfels has very low sulfide content, and the biotite zone has moderate amounts of copper and sulfur, decreasing outward. The chlorite zone is characterized by an abrupt increase in zinc and manganese content. Fluid-inclusion data suggest temperatures between 300° and 400°C for hydrothermal fluids in the biotite-chlorite zone of the porphyry and 250° to 300°C for fluids in the quartz-sericite-pyrite zone. Pressures equivalent to about 1.5 km of burial are indicated.

Río Víví district↗
USGS1974

New seismic study begins in Puerto Rico

A new seismological project is now underway in Puerto Rico to provide information needed for accurate assessment of the island's seismic hazard. The project should also help to increase understanding of the tectonics and geologic evolution of the Caribbean region. The Puerto Rico Seismic Program is being conducted by the Geological Survey with support provided by the Puerto Rico Water Resources Authority, an agency responsible for generation and distribution of electric power throughout the Commonwealth. The Program will include the installation of a network of high quality seismograph stations to monitor seismic activity on and around Puerto Rico. These stations will be distributed across the island to record the seismicity as uniformly as possible. The detection and accurate location of small earthquakes, as well as moderate magnitude shocks, will aid in mapping active seismic zones and in compiling frequency of occurrence statistics which ultimately wil be useful in seismic risk-zoning of hte island.

Puerto Rico↗
USGS1974

Dendritic dry valleys in the cone karst of Puerto Rico

The depressions in the cone karst (Kegelkarst) of the area west of Ciales in the Lares Limestone are alined in dry valleys that have dendritic patterns. These valleys apparently record the former existence of a cover of noncalcareous clastic material that was deposited on the limestone in late Tertiary time. One system of dendritic dry valleys ends at an abandoned meander of the Rio Grande de Manati, which is about 60 m above the present floor of the river. Another system leads to large masses of "blanket sand" near the town of Florida. These valleys were apparently eroded during the late Pliocene or very early Pleistocene when sea level was at least 80 m higher than it is today.

Puerto Rico↗
USGS1973

Porphyry copper deposits in Puerto Rico and their relation to arc-trench tectonics

The study of porphyry copper deposits in islands arcs provides an opportunity to observe closely the direct relationship between tectonics and ore deposition, and to avoid such complications as multiple orogenies and contamination of magmas that are common to deposits on continental margins. Puerto Rico has proved to be an ideal laboratory to make these observations. In the west central part of the island 240 million tons of .7 to .8 percent copper ore has been proved up in three deposits (Lutjen, 1971). Although deep saprolite covers most of the mineralized area, two marginal deposits, Helecho and Sapo Alegre, are partly exposed by deep stream valleys. The U. S. Geological Survey, in cooperation with the Puerto Rico Department of Natural Resources is in the middle of a five year geologic and geochemical study of copper deposits in the island. Drill core was made available through the courtesy of Kennecott Copper Corporation, American Metals Climax Corporation and the Puerto Rico Mining Commission. I wish to acknowledge the help of the Puerto Rico Laboratory of Geology for the chemical work, and Richard Marvin and J. Thomas Nash of the USGS for geochronologic and fluid inclusion data, respectively. This report will briefly describe the porphyry copper deposits of Puerto Rico and their tectonic-chronologic position in the development of the Greater Antilles. By extrapolation from this data it will be suggested that these deposits and several others are related to a process of subduction zone deactivation.

Open-File Report↗
USGS1973

Geology of a system of submarine canyons south of Puerto Rico

A strongly dendritic submarine canyon system with four major canyons occupies a 30-km indentation in the insular shelf off the south coast of Puerto Rico between Guanica and Ponce. Each canyon has several headward branches at depths of 100 to 1,100 m. Each of the five major rivers that reach the coast between Guanica and Ponce is opposite a canyon head, and off each of the rivers a channel 20 to 30 m deep is incised into the insular shelf. The entire canyon system is 40 km long and terminates at a depth of about 3.3 km; no fan or other constructional feature appears to have been formed. A 410-km continuous seismic profiling survey shows that three unconformable stratigraphic units underlie the canyon area. One sample of indurated clay of probable Miocene age was dredged from a canyon-wall outcrop of the middle stratigraphic unit. The three stratigraphic units may be roughly correlative with (in ascending order) the Juana Diaz Formation, the Ponce Limestone, and an unnamed upper section found in a nearby drill hole ashore. Canyon-axis sediment at depths of 700 to 2,200 m is entirely of pelagic origin, indicating that sediment is not now being transported down the canyons.

Guanica, Ponce↗