The Gem Park Complex (a new name in this report), which lies about 11 miles northwest of Westcliffe, Colo., is a small funnel-shaped composite body related to the McClure Mountain Complex a few miles to the northeast. The Gem Park Complex consists mostly of pyroxenite and gabbro with minor dikes and bodies of lamprophyre, syenite porphyry, and nepheline syenite pegmatite, and abundant dikes and irregular bodies of carbonatite, all of Cambrian age. A mass of fenite lies near the center of the complex. The whole complex lies discordantly in Precambrian gneissic terrane and is overlain by Tertiary volcanic rocks. Large areas in the complex are covered by Quaternary alluvium and colluvium. Some carbonatite dikes and fenite contain concentrations of niobium, rare-earth elements, thorium, phosphorus, some other elements, and vermiculite. The arrangement of carbonatite dikes, the position of the fenite, and other features suggest that a large carbonatite body lies beneath the surface near the center of the complex.

This report on the geochemistry of niobium and tantalum is chiefly a summary of works published since those of Rankama, and it is not a product of original research. It summarizes what is known of the geochemical characteristics of these elements and their occurrence in various types of minerals, rocks, and ores. A

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Basalts from the upper 255 meters of the oceanic crust at Site 396B show moderately large variations in petrography, mineralogy, and chemistry. The upper part of the section comprises aphyric basalt with rare, rounded plagioclase phenocrysts and lesser amounts of olivine. The central part of the section is olivine and plagioclase phyric with modal abundances ranging from about 10 to 30 per cent. The lowest part of the sequence is moderately phyric with widely varying abundances of olivine and plagioclase phenocrysts. Clinopyroxene phenocrysts occur in only one rock. Co-existing olivine and plagioclase phenocrysts exhibit both normal and reverse zoning which suggests mixing of different magma batches prior to eruption. Major and trace element compositions of glass and whole rock basalt samples from Hole 396B suggest the following: a) The two major basaltic magma types are a Ti-poor, Ca-rich ("X") type and Ti-rich, Ca-poor ("Y") type. b) Different magma batches may represent separate fractions of the same differentiating parent liquid, or may reflect fractionation "events" acting upon similar or distinct liquid compositions. In either case, eruptive products of any one batch show a characteristic chemistry and lithology. c) Different magma batches appear to have been erupted in a contiguous time sequence except for minor amounts of extreme differentiates interlayered with lavas from unrelated batches. However, eruption of different batches deriving from a single liquid type may be separated by relatively large time intervals. d) "X"-type and "Y"-type liquids are characterized by different low pressure crystal-liquid phase equilibria. Plagioclase apparently precipitated at higher temperatures compared to olivine and clinopyroxene, for equivalent MgO content in "X"-type than in "Y"-type liquids. e) Leg 46 basalts generally have higher Na, Ti, and large ion lithophile (LIL) element abundances for equivalent MgO content than basaltic magmas from other parts of the Mid-Atlantic Ridge (e.g., FAMOUS). We tentatively suggest that these differences reflect lower degrees of partial melting at 22°N and are a reflection of ambient geothermal conditions.

Mafic and ultramafic rocks form a small layered funnel-shaped intrusive complex, including several smaller associated discordant intrusions, within Precambrian metamorphic rocks in the vicinity of Iron Mountain, northern Wet Mountains, Colo. The mafic rocks consist of several gradational varieties of gabbro, pyroxenite, dunite, anorthosite, and magnetite iron ore and are made up principally of bytownite-labradorite, monoclinic pyroxene, magnesiumrich olivine, and titaniferous magnetite. Brown amphibole, probably kaersutite, is a late-stage primary mineral.Part of the mafic complex is well layered, having originated through crystal settling in mafic magma. Conspicuous textures and structures that are characteristic of sedimentary rocks are graded bedding, crossbedding, and scour-andfill. Discordant bodies of pyroxenite and anorthosite intrude the layered rocks and offer evidence that later differentiation had proceeded below or beyond the chamber in whch the layered rocks accumulated. The mineralogic and chemical nature of the rocks and their close association with alkalic rocks of the McClure Mountain Complex indicate that these mafic and ultramafic rocks and the alkalic rocks are comagmatic.

Deposits of alunite in the J.farysvale region, Utah, are nearly all confined to the Bullion Canyon Volcanics of Tertiary age. The deposita consist of two types, alunite veinB and iegular alunite replacement bodies. Tile vein deposits are restricted to the vicinity of Alunite Ridge southwest of l1arysvale in the Tushar !bmtains, and the repla,..ement bodies are distributed circumferentially about a quartz monzonite etock in the Antelope Ranee northeast of the village.The wall rock alteration that borders the alunite veins has been divic'ed into three phases . In order of their zonal distribut ion toward the vein, the phases are the feeble phase, the moderate phase, and the intense phase. Feeble phase alteration is characterized by illite-montrnorillonite mixed lattice clay, kaolinite and minor quartz t-thich were formed at thv expense of carbcnate, seritized plagioclase and some of ((? the chlorite of the re 1 ional.ly al tcred Bullion Canyon volcanics.Alteration of the moderate phase is represented by tm assemblage, alunite, kaolinite and quartz which were produced in part from the mixed lattice clay am chlorite of the feeble phase. Strongly alunitized am silicified rock adjacent to the vein represents the intense phase of alteration.Alteration in the replacement deposits is represented by the feeble and moderate phases. The alunite bodies represent the moJerate phase of alterat.ion, and those bodies that are sharply defined are surro~"'lded by an envelope of feeble phase alteration. The mineralogy of the corresponding alteration phases of t he vein and replacement deposits is the S

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