Boron is a biologically important element, but its distribution in the natural environment and its behavior during many geological processes is not fully understood. In most metamorphic and igneous environments, boron is incorporated into minerals of the tourmaline supergroup. In high-grade metamorphic terranes like that of the Adirondack region of northern New York State, uncommon rock compositions combined with unusual and variable geologic conditions resulted in the formation of many additional boron-bearing minerals. This paper reviews the occurrences and geological settings of twelve relatively uncommon boron-bearing minerals in the southern Grenville Province of upstate New York and provides new chemical and Raman spectral data for seven of these minerals. The boron minerals range from relatively simple metal borates (e.g., vonsenite), to chemically complex borosilicates (e.g., prismatine), to a relatively rare borosilicate-carbonate (e.g., harkerite). Some are of primary igneous origin, while others are formed by a variety of prograde and retrograde metamorphic processes or by metasomatic/hydrothermal processes. Most of the boron minerals are formed within, or adjacent to, metasedimentary lithologies that surround the anorthositic massifs of the central Adirondacks. The metasedimentary rocks are thought to be the source of most of the boron, although additional boron isotope studies are needed to confirm this and to constrain the mechanisms of the formation of these unusual minerals.
Exposures of tremolite, fluor-uvite, and associated minerals along an east-west-trending ridge of Precambrian crystalline rocks south of Selleck Road near the village of West Pierrepont constitute ...
ABSTRACT Warwickite has been discovered in the Edwards and Balmat #3 mines in the Balmat-Edwards mining district, St. Lawrence County, New York, located in the Adirondack Lowlands. The samples from the two mines are similar in chemistry and atomic arrangement but differ chemically from previously described samples; they are among the most Fe-poor samples described to date. The warwickite in the Edwards Mine sample occurs as 1–2 mm-diameter green crystals associated with pink spinel, forsterite, phlogopite, and pyrite in an impure dolomitic marble, whereas warwickite in the specimens from the Balmat #3 mine, approximately 10 km distant, occurs as brown to amber colored, slender, elongate, millimeter-size crystals in a calcitic marble in association with pink spinel, phlogopite, anhydrite, pyrite, and galena. Chemical analyses of the two specimens by electron microprobe show similar empirical formulas of (Mg1.43Ti0.36Al0.18Cr3+0.02Zr0.01)Σ2.00B0.98O4 (Edwards Mine) and (Mg1.39Ti0.40Al0.18Cr3+0.01Zr0.01Fe2+0.01)Σ2.00B0.94O4 (Balmat mine). The atomic arrangement of a specimen from each mine was determined, and the high-precision refinements provide new insight into the warwickite structure. The M1 site in warwickite is split into two sites to accommodate two occupants with differing bonding requirements; the M1 site contains Mg and the M1′ site hosts Ti, with the two sites being separated by approximately 0.2 Å. The optimized structural formula for both warwickite samples is similar to [M1(Mg0.84Al0.14Ti0.024+)2.74M1′(Ti0.914+Mn0.082+Mg0.01)1.30]Σ4.04M2(Mg0.86Al0.10Ti0.044+)4.00B4O16], demonstrating ordering of Mg at M1 and M2 and Ti at M1′. The site-splitting demonstrates how divalent Mg and tetravalent Ti can exist at a site in solid solution by ordering the two cations at split sites.
Early Proterozoic ( Aphebian) sedimentary and volcanic rocks in Labrador are described from two tectonic belts: the Churchill Province of western Labrador, and the Makkovik Subprovince of eastern Labrador. The Aphebian in the Churchill Province is represented mainly by the Labrador Trough ( Kaniapiskau Supergroup) but also in the Laporte Croup, Lake Harbour Formation and Petscapiskau Croup. The Labrador Trough is the most completely exposed of these sequences and displays a transition {rom shelf sedimentation in the west, to deeper water basinal conditions in the east. Rifting along the eastern margin of the Labrador Trough may have produced a narrow proto-oceanic rift during this stage. Aphebian sequences in the Makkovik Subprovince are represented by the Maran Lake and Aillik groups. The Maran Lake and lower Aillik groups were deposited in environments broadly similar to those of the Churchill Province and in approximately the same time. The upper Aillik Group (17 50-1670 Ma) represents a younger assemblage dominated by f elsic volcanics intricately intruded by granites and may indicate the onset of radically diff erent tectonic conditions towards the end of Aphebian time.
Numerous localities of specular hematite have been found in the Grenville Province in St. Lawrence County, New York. Here, we focus on six of them: the Dodge mine, the Chub Lake prospect, the Toothaker Creek prospect, the Bowman prospect, the Whitton prospect, and the Toothaker Pond prospect. We used literature research, interviews, and personal observations to establish the history of each site as a source of mineral specimens. We examined extensive holdings of specimens from each site in the New York State Museum. We used sight identification, chemical tests, x-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy as necessary to identify all the mineral species present. We had determinations made of the stable oxygen isotope content of quartz, hematite, and calcite from the Chub Lake prospect, reported as 18O relative to Vienna Standard Mean Ocean Water (VSMOW). We conclude that these occurrences formed from groundwaters at a temperature of about 170 °C in areas of low topography on the surface of the Precambrian basement rocks. Two hypotheses for this process are presented and evaluated. Well-crystallized specimens of bladed specular hematite and Cumberland-habit quartz are the most common minerals found. Noteworthy accessory crystallized minerals include barite, calcite, and goethite. All six deposits are relatively free of sulfides, so that secondary goethite formed from weathering of iron-rich carbonates at some sites. It is likely that more such deposits will be discovered in this region in the future.
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