Petrography and geochemistry of precambrian rocks from GT-2 and EE-1

Technical Report · Mon Aug 01 04:00:00 EDT 1977

DOI:https://doi.org/10.2172/7080705· OSTI ID:7080705

Laughlin, A W; Eddy, A

During the drilling of GT-2 and EE-1, 27 cores totaling about 35 m were collected from the Precambrian section. Samples of each different lithology in each core were taken for petrographic and whole-rock major- and trace-element analyses. Whole-rock analyses are now completed on 37 samples. From these data four major Precambrian units were identified at the Fenton Hill site. Geophysical logs and cuttings were used to extrapolate between cores. The most abundant rock type is an extremely variable gneissic unit comprising about 75% of the rock penetrated. This rock is strongly foliated and may range compositionally from syenogranitic to tonalitic over a few centimeters. The bulk of the unit falls within the monzogranite field. Interlayered with the gneiss is a ferrohastingsite-biotite schist which compositionally resembles a basaltic andesite. A fault contact between the schist and gneiss was observed in one core. Intrusive into this metamorphic complex are two igneous rocks. A leucocratic monzogranite occurs as at least two 15-m-thick dikes, and a biotite-granodiorite body was intercepted by 338 m of drill hole. Both rocks are unfoliated and equigranular. The biotite granodiorite is very homogeneous and is characterized by high modal contents of biotite and sphene and by high K/sub 2/O, TiO/sub 2/, and P/sub 2/O/sub 5/ contents. Although all of the cores examined show fractures, most of these are tightly sealed or healed. Calcite is the most abundant fracture filling mineral, but epidote, quartz, chlorite, clays or sulfides have also been observed. The degree of alteration of the essential minerals normally increases as these fractures are approached. The homogeneity of the biotite granodiorite at the bottom of GT-2 and the high degree of fracture filling ensure an ideal setting for the Hot Dry Rock Experiment.

• Research Organization: Los Alamos Scientific Lab., N.Mex. (USA)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 7080705
• Report Number(s): LA-6930-MS
• Country of Publication: United States
• Language: English

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15 GEOTHERMAL ENERGY
150201* -- Geology & Hydrology of Geothermal Systems-- USA-- (-1989)
150302 -- Geothermal Exploration & Exploration Technology-- Geochemical Techniques & Surveys
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
ALUMINIUM SILICATES
BIOTITE
BOREHOLES
CALCITE
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CALCIUM OXIDES
CALCIUM SILICATES
CALDERAS
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CARBONATES
CAVITIES
CHALCOGENIDES
CHEMICAL COMPOSITION
CHLORITE MINERALS
CLAYS
DRILL CORES
DRILLING
EPIDOTES
EXPLORATION
GEOCHEMICAL SURVEYS
GEOLOGIC AGES
GEOLOGIC FAULTS
GEOLOGIC STRUCTURES
GEOLOGICAL SURVEYS
GEOLOGY
GEOTHERMAL EXPLORATION
GRANITES
GRANODIORITES
Geothermal Legacy
IGNEOUS ROCKS
IRON COMPOUNDS
IRON OXIDES
IRON SILICATES
JEMEZ MOUNTAINS
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
MANGANESE COMPOUNDS
MANGANESE OXIDES
MICA
MINERALS
MOUNTAINS
NEW MEXICO
NORTH AMERICA
OXIDES
OXYGEN COMPOUNDS
PETROLOGY
PHOSPHORUS COMPOUNDS
PHOSPHORUS OXIDES
POTASSIUM COMPOUNDS
POTASSIUM OXIDES
PRECAMBRIAN ERA
QUARTZ
ROCK DRILLING
ROCKS
SILICA
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
SODIUM COMPOUNDS
SODIUM OXIDES
STRONTIUM COMPOUNDS
STRONTIUM OXIDES
SULFIDES
SULFUR COMPOUNDS
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRACE AMOUNTS
TRANSITION ELEMENT COMPOUNDS
USA