Relationship of pegmatites to U-Th mineralization in Precambrian crystalline rocks near Easton, Pennsylvania

Conference · Mon Mar 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:6035066

Brand, C C; Malinconico, Jr, L L ^[1]; Tepper, J H ^[2]

---

1. Lafayette College, Easton, PA (United States). Dept. of Geology
2. Union College, Schenectady, NY (United States). Dept. of Geology

Previous studies have shown that high radon levels in the Easton area are not simply confined to the igneous crystalline rocks of the Reading Prong. Since the radon is the result of the decay of uranium/thorium bearing minerals, the question then is where are these minerals hosted. Two hypotheses have been proposed for the origin of this mineralization: (1) derivation from an acidic magma during a hydrothermal stage of pegmatite intrusion, or (2) synsedimentary deposition in reducing, oceanic waters with subsequent crystallization of uraninite during metamorphism. The goal of the present study is to determine which process(es) were responsible for the mineralization and to determine where the uranium and thorium are hosted in the Precambrian rocks in the Easton area. Gamma surveys at three locations have demonstrated high radioactivity levels associated with the pegmatites (8,000--750,000 C/min.). Despite the fact that the host rocks and surrounding Paleozoic carbonates have been shown to have high levels of radon, the authors have measured significantly lower radioactivity levels (3,000--8,000 C/min.) in these rocks. The radioactivity levels tend to be high a very short distance into the host and then decrease very rapidly away from the pegmatites. The migmatitic regions in the Byram gneiss (20,000--60,000 C/min.) are considerably higher than the rest of the gneiss (8,000--12,000 C/min.) suggesting remobilization of U-Th during partial melting. These data tend to support the hypothesis that most of the radon is derived from the decay of elements concentrated in the igneous rocks, which subsequently migrated into the host rocks.

• OSTI ID: 6035066
• Report Number(s): CONF-9303211--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:2
• Country of Publication: United States
• Language: English

Related Subjects

050100* -- Nuclear Fuels-- Reserves
Exploration
& Mining
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
54 ENVIRONMENTAL SCIENCES
540230 -- Environment
Terrestrial-- Radioactive Materials Monitoring & Transport-- (1990-)
ACTINIDES
CHEMICAL COMPOSITION
DECAY
DEVELOPED COUNTRIES
ECOLOGICAL CONCENTRATION
ELEMENTS
FLUIDS
GASES
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOPHYSICAL SURVEYS
GNEISSES
IGNEOUS ROCKS
MATERIALS
METALS
METAMORPHIC ROCKS
MINERALIZATION
MINERALS
NONMETALS
NORTH AMERICA
OXIDE MINERALS
PEGMATITES
PENNSYLVANIA
PLUTONIC ROCKS
PRECAMBRIAN ERA
RADIOACTIVE MATERIALS
RADIOACTIVE MINERALS
RADIOMETRIC SURVEYS
RADON
RARE GASES
ROCKS
SURVEYS
THORIUM
URANINITES
URANIUM
URANIUM MINERALS
USA