Non-commercial quantities of inflammable gas were found in small vugs and fractures in metamorphosed Grenville (pre-Cambrian) magnesian limestone in the 900- and 1,500-foot levels of the zinc mine at Edwards, St. Lawrence County, New York. The most significant minerals found in the openings containing the gas are salt and gypsum. The geological evidence seems to suggest a natural organic derivation similar to that of commercial accumulations in younger rocks.
The isotopic composition of the lead minerals from the Balmat Area was determined by standard mass spectrographic methods. The results and sample descriptions are tabulated. The isotopic composition indicates a Precambraian age. According to the latest estimate of lead isotope evaluation in the earth's crust model, the age of deposition is 1050 the J-57 engine 100 million years.
Assembling of scattered data regarding the lead of pegmatites, granitic rocks and associated lead ores yields some significant facts and deductions. Pegmatitic feldspars contain two to twenty times as much lead as granites or their feldspars. The lead in major pegmatites commonly duplicates ore lead isotopically, whereas the lead of granites associated with lead ores is much more variable and often distinctly anomalous. These data do not support the common assumption that ores are derived from igneous rocks by a process of magmatic differentiation. Indeed, they justify the suspicion that pegmatites may not be an end product of differentiation, but instead may result from the external addition of a mineralized fluid to the margins of a cooling intrusive along fracture zones, the reaction producing a low melting eutectic of granitic base with exotic accessories. The few data available for minor pegmatites suggest that their lead is more variable, possibly indicative of diverse origins.The meager data on lead in sedimentary rocks and in igneous rocks outside the granite family are inconclusive. Some appear to contain normal lead and others clearly are anomalous.
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