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Aluminum is found mostly in silicates (micas, garnets, pyroxenes, feldspars, and amphiboles) at both localities. High-temperature ores have some aluminum in gahnite and some in franklinite. In the marble, aluminum is hosted by spinel, corundum, tourmalines, micas, and other minerals.
Antimony is rare locally, but is found in romeite, yeatmanite, and some sulfosalts, especially in zinkenite at Sterling Hill, a major host.
Arsenic occurs in arsenopyrite in the Franklin Marble and in loellingite in both orebodies. It is locally abundant in the nickel-arsenide assemblage and in apatite-group minerals, both from Franklin. Six manganese arsenosilicates, with arsenic in varying oxidation states, are found locally. Arsenic is present in small quantities in secondary arsenates of Mn and other cations in secondary veins at Sterling Hill.
Barium predominantly occurs in barite, which is widespread in minor amounts at Franklin and also is known from Sterling Hill. Barium also is hosted by micas and by feldspars at Franklin, chiefly hyalophane; it was largely unsought by analysts and may occur in apatites, carbonates, and layer silicates.
Beryllium is found in barylite, in the rare minerals samfowlerite and wawayandaite, and possibly as small quantities in vesuvianite; otherwise it is of trivial significance locally, but is a common trace element. Some beryllium is possible in willemite, which is isostructural with phenakite.
At Franklin, manganaxinite is the principal boron host; at Sterling Hill, sussexite is. Less common is datolite, found locally at Franklin but not Sterling Hill. Minor boron-containing minerals occur at both localities. The Franklin Marble is also host to boron, in fluoborite, uvite, and other minerals.
Cadmium is present in minor amounts in sphalerite and is found in the secondary minerals hawleyite and greenockite. Little is known of its distribution.
Calcium is widely distributed in both carbonate and silicate minerals. The Franklin Marble is impure, but mostly calcite, and calcite is almost ubiquitous in the orebodies. Calcium silicates are very common at Franklin, but less so at Sterling Hill, except for clinopyroxenes. Much calcium is present as a minor element in other minerals.
All local carbon is present as carbonate or as graphite, except that which occurs in scapolite in the Franklin Marble, and as hydrocarbons in local limestones. The overwhelmingly dominant carbonate mineral is calcite (see above), but carbonates of magnesium and manganese occur in both orebodies.
Chlorine is found in nasonite, turneaureite, and hedyphane and is likely hosted in minor amounts by many of minerals in the apatite-, scapolite-, and friedelite-groups.
Chromium is a minor element locally and was largely unsought in analyses. It is known in minor amounts in gahnite, margarite, corundum, and hercynite, all from one occurrence at Sterling Hill.
Little is known of cobalt distribution; it was found in the dendritic extremities of the nickel-arsenide assemblage and occurs very rarely as erythrite in secondary assemblages at both deposits. Cobalt may be hosted by arsenopyrite and loellingite, but this is unproven locally.
Local copper occurs as chalcocite and other sulfides and in trivial amounts in secondary minerals (carbonates, arsenates, sulfates) derived therefrom. Native copper occurs widely and finely disseminated in Franklin ores and calcium silicates.
Fluorine is very common in the accessory minerals of the Franklin Marble, especially in silicates. Fluorite is not uncommon in the Franklin orebody. The geochemical distribution of fluorine is but barely studied. General observations were given by Kearns (1977) and Buis (1983).
Gallium is a minor element locally; the occurrences were reviewed by Papish and Stilson (1930).
Gold is found only in trivial quantities and is uncombined with other elements.
As hydroxyl, hydrogen is present in the primary ores in leucophoenicite and the manganese-humites. In calcium silicate units, it is abundant in micas, amphiboles, and many other species. Many of the rare and unusual minerals contain hydroxyl, and some are also hydrated.
Iron is abundant in the orebodies, but is present only in minor amounts in the Franklin Marble in arsenopyrite, pyrite, and other sulfides and as a substituent for Mg in spinels and amphiboles. Loellingite is a moderately common accessory mineral in the orebodies. Within the ore assemblages iron is predominantly ferric, except in olivine- and humite-related minerals. The dominant host for Fe at both deposits is franklinite. Magnetite is of less significance, and hematite even less so. At Franklin, andradite is the major silicate host, in part capturing available reactive iron by rimming franklinite. Some iron is hosted by amphiboles and clinopyroxenes; iron silicates are otherwise very rare at Franklin. At Sterling Hill, much fayalite is found in the black willemite zone. Ferrian grossular is known, but andradite is perhaps less common. In general, silicates which are not Fe-dominant host more iron at Sterling Hill than at Franklin. Iron was of economic significance historically and was later used to make spiegeleisen.
In general, relative to most zinc ore deposits, these deposits are very low in lead content. Galena is a common, albeit minor constituent of the Paleozoic sulfide veins, and is rarely found as galena in pods near the hanging wall at Franklin. Principal primary hosts for Pb at Franklin are esperite and hardystonite, the latter containing small but pervasive amounts of non-essential lead. In a localized occurrence, lead is found in the suite of restricted lead silicates. Lead is hosted by hedyphane in secondary vein assemblages at Franklin and is a common trace element in calcite. In general, specific lead minerals are much less abundant at Sterling Hill than at Franklin. However, there was 3-4 times as much lead in the ore concentrates from Sterling as there was in those from Franklin, resulting from the higher lead-content of Sterling Hill calcite. There is a halo of lead in the Franklin Marble surrounding both orebodies. See the discussion of the “lead problem” in the section entitled “Beneficiation of the zinc deposits.”
Magnesium is common within the Franklin Marble in dolomite, spinels, humites, amphiboles, and accessory silicates, and within the orebodies in silicates and carbonates. In high-temperature assemblages at Franklin, magnesium is predominantly hosted by amphiboles, clinopyroxenes, and micas; at Sterling Hill, it is hosted predominantly by amphiboles, micas, magnesian tephroite, manganese-humites, and clinopyroxenes. Magnesium silicate plays an important role in the east limb at Sterling Hill, replacing many of the original minerals with serpentine and, less commonly, with talc. The magnesioriebeckite-lennilenapeite assemblage at Franklin is anomalous but noteworthy.
Together with iron and zinc, manganese occurs widespread in franklinite at both deposits. Together with calcium and/or zinc, and unlike iron, it locally forms a large number of silicate minerals, and is a very common, minor substituent in minerals which do not have essential manganese. Manganese, as Mn2+, is abundant in franklinite and in the high-temperature primary silicate assemblages, in particular in the olivines, Mn-humites, and pyroxenoids. Although a minor constituent by weight percent, the manganese content of willemite and zincite is substantial in gross amount. Manganese is pervasive locally, occurring as an essential element in 43 silicates, and is predominantly divalent, entering almost all orebody minerals where crystal structures permit it. Oxide minerals are a major host, and manganosite is known from Franklin. Pyrochroite and cianciulliite are the only Mn2+-OH minerals found locally. Trivalent manganese is not rare; it is found in moderate abundance in hetaerolite and jacobsite and in lesser amounts in minerals such as hancockite. Aside from these, trivalent Mn occurs in trivial minerals at Franklin (Dunn et al., 1991). Quadrivalent Mn is known in abundance in chalcophanite and in todorokite, woodruffite, and related oxides, but is restricted spatially, being found in weathered occurrences in which it is partitioned from iron. Manganese is highly mobile and occurs in a large number of secondary vein minerals, the most notable of which are layer silicates and manganese arsenates at both deposits. Manganese had local economic significance as a constituent of spiegeleisen.
Molybdenum is found principally in molybdenite, powellite, and scheelite, but it is not common locally.
Nickel occurred in abundance but once: in the nickel-arsenide assemblage at Franklin. It was largely unsought in chemical analyses, but is a common trace element.
Oxygen occurs in vast abundance here, in both the marble host and in the orebodies, which are in part uniquely defined by the presence of much oxygen.
Phosphorus is common only in arsenian fluorapatite from Franklin; almost no secondary phosphates are known there.
Potassium is largely hosted by feldspars and micas at both deposits; little information exists on distribution.
Rare-earth elements occur predominantly in allanite in microcline pegmatite at Franklin. Primary Franklin allanite shows cerium-dominance. Although not sought by analysts, rare-earth elements are possibly hosted by the apatite group; the matter is largely unstudied to date. Some secondary arsenates contain lanthanum and neodymium, in retzian-(La) and retzian-(Nd), respectively.
Scandium is present chiefly in franklinite and andradite (Frondel, 1970) and also in augite and the rare mineral thortveitite.
Silicon is grossly abundant, forming a major part of both orebodies as silicate minerals, and occurs within the ores in willemite, tephroite, leucophoenicite, and the Mn-humites. Significantly, quartz is uncommon to rare here except in the country rocks.
Silver is a minor metal here, found in the native state with chalcocite and magnetite. Palache (1935) reported a New Jersey Zinc Company determination that Ag is present in spectrographic analyses of many Franklin minerals.
Sodium is found in albitic feldspars and in the amphiboles and pyroxenes, but less so in the micas. Best known in the marsturite-ganophyllite assemblage from Franklin, it also occurs in uncommon zeolite assemblages.
Strontianite and celestine are the only strontium-essential minerals here. Strontium is hosted by hedyphane in secondary assemblages. It was largely unsought by analysts, and its distribution is unknown.
Compared with most other zinc deposits, the sulfur content of these deposits is very low. Sulfides occur in late Paleozoic veins; additionally, chalcocite is not uncommon in the orebodies. The preponderance of local sulfur is present as ZnS (sphalerite), uncommon at Franklin, but found in substantial quantities at Sterling Hill.
Titanium has been little sought; it is found in some oxides, chiefly pyrophanite and ilmenite, both uncommon locally, and brookite and rutile, and may be hosted in micas or pyroxenes. Titanite is a titanium host in the marble.
Tungsten is found in scheelite and some powellite and is a minor element locally.
Uranium is very rare locally, occurring in uraninite. The radioactivity of local minerals was studied by Keevil (1950).
Found in trivial amounts in descloizite, pyrobelonite, and goldmanite, vanadium has not been otherwise studied; it may occur in pyroxenes.
There are no yttrium-essential minerals found here. Yttrium follows the rare-earth elements in allanite, some arsenates, and presumably in some apatites; much study remains to be done.
Zinc is widespread and pervasive; it is a major constituent of all three zinc ore minerals, and 47 zinc minerals are known here. Approximately 6.5 million tons of zinc were obtained from these deposits. In general, species with essential zinc are more widespread at Franklin than at Sterling Hill. The geochemistry of zinc was discussed by Neumann (1948). In all local minerals which have essential zinc, it is tetrahedrally coordinated, with the exception of hendricksite, sclarite, and petedunnite, in which it is octahedrally coordinated.
The dominant silicate host for zinc is willemite. Truly vast amounts of zinc are present in this ore mineral, which contains approximately 52 wt. % Zn. Zincite, although not abundant, contains approximately 80 wt. % Zn.
As a subordinate substituent in solid solution in many silicates, zinc is octahedrally coordinated. Very substantial quantities of zinc are thusly held in tephroite and manganese-humites in the ores, and in diopside, hendricksite, rhodonite, augite, and other
minerals in the calcium silicate units. Zinc is present locally in minerals in nearly all the major anionic groups: in sphalerite as a sulfide; in smithsonite, sclarite, and loseyite as carbonates; and in zincite, franklinite, hetaerolite, gahnite, and other species as oxides. It also forms numerous arsenates and 22 silicates. The unique local association with manganese defines many of the unique and interesting minerals found here.
The orebodies present ideal “laboratories” in which to examine in detail the as yet unstudied behavior of zinc in calcium silicate units and other assemblages.
Zircon is the only zirconium-essential mineral found here. Zirconium has been unsought in analyses, but is likely common in minor amounts within the pegmatites.
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| Copyright © 1995 by Pete J. Dunn |
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by Herb Yeates
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