Talc Deposits Research Articles

Mineralogy and origin of the State Line talc deposit, Pennsylvania

The State Line talc deposit, in Lancaster County, Pennsylvania, near the Maryland border, occurs at the boundary between a serpentinite body and surrounding metamorphosed pelitic rocks. Blackwall-type zones are found in the talc body. The zones are composed of variable amounts of tremolite, chlorite, biotite, and dolomite. However, trace element chemistry indicates that the zones are not a product of simple blackwall metasomatic processes. The ratios of Al 2 O 3 /Cr, Zr/Cr, Ti/Cr, and Al 2 O 3 /Ni in the blackwall-type zones are intermediate between the ratios found in the serpentinite and the pelite, supporting the hypothesis that these zones result from the sedimentary mixing of pelitic and serpentinite-bearing material on the sea floor, with later modifying metasomatism.The distribution of tremolite, a contaminant that affects significantly the market value of a talc deposit, is the result of small-scale metasomatic reactions that modified the original layers of serpentinite-bearing and pelitic detritus; and larger scale metasomatism involving silica, water, and carbon dioxide that fixed tremolite as the saturating calcium phase in the proximity of the pelitic country rock, and dolomite in the proximity of the serpentinite.

Formation of the talc deposit of Kibanda (Rwanda) and its relation to the regional metamorphic evolution

Kibanda, one of the most important talc deposits in Rwanda, is located in a suite of metasediments and volcanics of the Kibara Supergroup. These are polymetamorphosed rocks belonging to the Kibuye Formation. The coexistence of oligoclase/andesine and Al-rich hornblende in amphibolites indicates that amphibolite facies metamorphism was reached during Kibaran metamorphism. These amphibolites are derived from tholeiitic mafic volcanics with intraplate geochemical characteristics. A retrograde greenschist facies assemblage (albite, actinolite, chlorite, etc.) is also documented. The timing of this retrograde event is uncertain although K/Armineral ages of 490 Ma. from biotites prove the influence of a Pan-African “event”. Mica ages from the host rocks and elsewhere are within the range of 410 to 590 Ma. Stratiform metamorphosed carbonate layers enveloped in metabasic rocks have been affected by hydrothermal alteration introducing essentially Si into the system. Accordingly the talc schists exhibit all characteristics of carbonate hosted talc deposits without any signs of Mg-bearing fluids derived from mafic/ultramafic rocks. The dolomitic precursor reacting with these hydrothermal solutions was totally transformed into talc. After the total consumption of dolomite, quartz veins were formed due to the ongoing hydrothermal activity. Oversaturated highly saline NaCl-CaCl 2 fluid inclusions, giving T h from 175–350°C and salinities of 30.7–38.7% NaCl equ. are documented from these quartz veins. These events also produced a hydrothermal aureole of chlorite schists with voluminous mobilization and mass exchange. The formation of the talc deposit is suggested to be related to the thermal activity of the granite intrusions or to the retrograde metamorphic event.

Petrogenesis and timing of talc formation in the Ruby Range, southwestern Montana

Talc deposits in the Ruby Range, southwestern Montana, have formed in Archean dolomitic marbles that were mineralized during retrograde talcification in the Proterozoic. Calcite-rich marbles contain the assemblage calcite-olivine-phlogopite + or - tremolite, indicating that metamorphism occurred in the upper amphibolite to granulite facies (M 1 ); crystallization of serpentine and chlorite, and dolomitization of the marbles in the greenschist facies overprinted the high-grade calc-silicate assemblages (M 2 ); and talc has replaced dolomite and the other greenschist-grade silicate minerals in the latest stage of recrystallization which resulted in the formation of the main talc bodies (M 3 ). Structural control of the talc formation is suggested by discontinuous occurrences of talc bodies along layer-parallel fractures. Preservation of relict textures indicates that the talc formed during constant volume replacement. Geochemical analyses and mass balance calculations demonstrate that introduction of large quantities of Si and Mg and removal of Ca is required to maintain constant volume. Model reactions indicate that infiltration of a minimum of 4.8 x 10 5 1 of water is needed to convert a cubic meter of the average high-grade marble to talc (volumetric water/rock ratio > 600). The infiltration mechanism is consistent with the observation that no isobaric univariant mineral assemblages were present to buffer the composition of the metamorphic fluids. Estimates of the maximum conditions of talc formation of 2 kbars and 400 degrees C are based on field observations and heterogeneous phase equilibria; it is probable that the talc actually formed at much lower temperatures and pressures, possibly in a near-surface hot spring deposit. Regional geologic relations indicate that the talc mineralization occurred during the middle Proterozoic.

Geochemistry and genesis of Austrian talc deposits

The lassing and Rabenwald tale deposits are, at present, the only economic occurrences in the Eastern Alps, producing 20,000 and 110,000 t/a, respectively. In spite of different tectonic settings, there are genetic similarities. Both deposits can be ascribed to hydrothermal alteration of preexisting carbonates during the Alpidic tectonic and metamorphic event. The tale ores of both deposits exhibit the geochemical features typical of carbonate-hosted talc deposits. The Lassing deposit is situated in an intensely tectonized section of the WNW-striking regional Liesing-Palten lineament, which is part of a well-developed system of Tertiary fracture zones in the Eastern Alps. Hydrothermal activity and temperatures in these fault zones increase from E to W approaching the central units (Penninic) of the Eastern Alps. Underground observations, as well as mineralogical and geochemical data obtained in the course of this study, reveal tale formation to be caused by the alteration of preexisting dolomites. Hydrothermal Si-bearing fluids altered these dolomites to talc schists. The Rabenwald deposit occurs in a different tectonic setting within gneisses of the Lower Austroalpine unit. Tale formation is linked to a distinct thrust zone with small relics of magnesite lenses in the tale chlorite schists. The established genetic interpretation, i.e. derivation of Mg-bearing solutions from ultramafic bodies in deeper tectonic units, is at variance with new geochemical and petrographical data. Trace element distribution at Rabenwald does not differ from that of carbonate-hosted talc deposits. Rabenwald is thus interpreted as a wedge of Upper Austroalpine Paleozoic rocks (especially magnesites) emplaced into the Lower Austroalpine gneisses during Alpine orogenesis and tectonism.

Talc deposition and effects after 20 days of repeated inhalation exposure of rats and mice to talc

The relationship between the inhalation exposure concentration of talc and the resulting lung burdens and histologic lesions was studied using groups of 20 F344/Crl rats and 20 B6C3F mice (10 male and 10 female) exposed to one of three concentrations of asbestos-free talc for 6 hr/day, 5 days/week for 4 weeks. Controls were exposed to filtered air using the same schedule. The pulmonary retention of talc and the development of pulmonary pathology were evaluated. The mass median aerodynamic diameter (MMAD) of the talc aerosol was 3.0 microns with a geometric standard deviation (sigma g) of 1.9. The mean exposure concentrations for rats were 0, 2.3, 4.3, and 17 mg talc/m3. Lung burdens in rats averaged 0, 0.07, 0.17, and 0.72 mg talc/g lung after the 20-day inhalation exposure; thus, the amount retained in the lung per unit of exposure concentration increased with increasing concentration. Mean exposure concentrations for the mice were 0, 2.2, 5.7, and 20.4 mg of talc/m3, which resulted in lung burdens of 0, 0.10, 0.29, and 1.0 mg talc/g lung; thus, the relationship between exposure concentration and the amount retained in the lung was approximately constant. Lung burdens from this study were used to project lung burdens that would result from longer exposures of rodents and man. No clinical signs were observed in the rats or mice prior to sacrifice 24 hr after the last exposure day. Histologic alterations in lung tissue consisted of only a modest, diffuse increase of talc-containing, free macrophages within alveolar spaces in both rat and mouse groups exposed to the highest level of talc for 20 days. A model simulating chronic talc inhalation exposure of rats and mice predicted lung burdens of 2-3 mg talc/g lung (wet wt) if animals were exposed to 17 mg talc/m3 for 2 years, and deposition and clearance of talc were unchanged by continued exposure. A potential limitation in this modeling is that if clearance of talc is delayed by continued exposure, the accumulated talc lung burdens would be higher than those projected by the simulation model. Humans exposed to aerosols of respirable talc are projected to accumulate much higher lung burdens than would occur in rodents exposed to the same aerosol, because humans have a higher estimated deposition fraction and slower estimated clearance of the deposited talc dust. Equilibrium lung burdens of greater than or equal to 2 mg talc/g lung were predicted for human exposures at or near the TLV for talc.

Mössbauer spectroscopy of talc minerals

By Mossbauer spectroscopy we investigated some talc, chloritoschist and micaschist samples drawn from the biggest Paleozoic talc deposit in Sardinia, Italy. Compared to results of previous chemical analyses some discrepancies exist. Data show the high degree of chloritization of neighbouring micaschist. This material exhibits the presence of primary ilmenite.

Mineralogy and geochemical dispersion in tropical residual soils overlying a talc deposit in southwestern Nigeria

Soil profiles overlying a talc deposit and associated amphibolite country rock have been investigated in order to determine the mineralogy and nature of geochemical dispersion, as a potential tool of industrial mineral prospecting in tropical terraines. Results of mineralogical analysis show that in soils overlying the talc body, talc still persists as a major component of the soil, in association with quartz, chlorite, illite and goethite, whereas in the amphibolite soil, most primary minerals have decomposed to kaolinite, quartz and goethite. Chemical variations in the soils are characterized by general enrichment in Fe 2O 3 and Al 2O 3, and depletion in Na 2O, K 2O, CaO, MgO and FeO relative to the parent rocks. Trace-element abundances show inconsistent patterns. While Ni and Co are depleted relative to the parent rocks, Zn and Cu show considerable enhancement. In spite of the intense weathering characteristics of tropical environments, high MgO contents of the soils seem to be the only reliable geochemical indicator of the existence of talc deposits beneath the soil cover. This parameter in conjunction with X-ray diffraction analysis of the soils may constitute an invaluable exploration tool for detecting buried talc deposits.

Electron Microscopic Analyses of Dust From the Lungs and the Lymph Nodes of Talc-Mine Employees

The primary purpose of the present study was to obtain microscopic analyses of the lung and lymph-node dust samples from 12 deceased Austrian workers who had been exposed occupationally to dust of talc and other mineral impurities in a talc deposit for many years. The results of the analyses of both fibers and particles are presented. A second goal of the study was to search for a relationship between different grades of pneumoconiotic effects and the concentration, size distribution and the chemical composition of the retained particles. Automatic analysis of approximately regularly shaped particles with a computer-controlled scanning electron microscope (CCSEM) was used for this purpose, while the fiber content was determined manually on the SEM-screen. The SEM examination of real and irregularly shaped fibers at a magnification of 6000x resulted in an average concentration that was increased slightly in comparison to that found in so-called normal lungs. Fibers were rather short with a mean length of 3 microns; 95% of the fibers had a length less than 10 microns. There was reasonable agreement between medical findings and mineralogical analyses concerning the grade of pneumoconiosis in most of the cases.

Sepiolite asbestos from franklin, new jersey: A case study in medical geology

Asbestiform sepiolite has been found in a zinc deposit at Franklin, New Jersey. The host rock is Precambrian Franklin marble. Pseudomorphous foliated texture and cross-cutting relationships indicate replacement of talc by sepiolite. Sepiolite is manganoan, while talc contains little manganese, suggesting differences in manganese substitution in these minerals and providing evidence against solid-state replacement. Sepiolite from Franklin is of moderate crystallinity and consists of soft, flexible mass-fiber. Comparison with other sepiolite samples suggests that increased crystallinity among sepiolites parallels increased fiber length, while disorder appears to be associated with flexibility. Length and aspect ratio (length/width) distributions support toxicological equation of asbestiform sepiolite with the regulated asbestos minerals. The data presented here suggest that talc can be unstable in a low-temperature hydrothermal environment, altering under certain conditions to form sepiolite. In a wider context, sepiolite may be expected to precipitate at the end-stages of hydrothermal mineralization in some talc deposits and in carbonate and calc-silicate rocks. Many occurrences of sepiolite in these rocks may have been overlooked due to similarities with other minerals. The fact that sepiolite has been previously unrecognized and misidentified at Franklin is a case in point. Since there is evidence suggesting that sepiolite is fibrogenic and carcinogenic, its potential occurrence in consumer talcs and crushed-stone products has environmental health implications. Similarities in composition and other analytical parameters may cause sepiolite to be mistaken for fibrous talc or chrysotile in environmental samples.

Ultramafic complexes and associated mineral deposits in the Precambrian of eastern Minas Gerais, Brazil

Based on field work, prospection and petrographic studies ultramafic complexes and their mineral deposits from eastern Minas Gerais in southeastern Brazil are generally outlined to form a basis for future investigations in this region. The bodies dealt with occur at Ipanema, Corrego Novo, Bela Vista de Minas, Rio Pomba and Liberdade. These ultramafic bodies are generally enclosed in high-grade gneisses and consist of serpentinized peridotites and harzburgites which were metamorphosed together with their country rocks in upper amphibolite to granulite facies. Weathering of these rocks gives rise to nickeliferous laterite, while metamorphism has resulted in anthophyllite asbestos and talc deposits.

Geology and geochemistry of the Chu Chua massive sulfide deposit, British Columbia

The deposit occurs in alkalic and transitional basalts of upper Paleozoic age formed in an oceanic island tectonic environment. Two major lensoid massive sulfide bodies composed mainly of pyrite and chalcopyrite are underlain by chemically precipitated massive siliceous, and talcose rocks. The composition and temperature of the hydrothermal solutions have been constrained by a consideration of observed mineral associations and relative stabilities of talc, pyrrhotite, pyrite, chalcopyrite, and magnetite. Based on these calculations, areas of talc deposition at Chu Chua are interpreted to represent the vents of the hydrothermal solutions on the sea floor. Owing to cooling and mixing of the talc-depositing solutions with normal seawater, silica and the sulfides also were precipitated. Lead isotope compositions of pyrite and chalcopyrite in the deposit are similar to those of the host basalts, suggesting that the basalts were most likely the source of metals in the hydrothermal solutions. It is proposed that chemically precipitated siliceous and talc rocks may be used as exploration guides for massive sulfides associated with basaltic rocks, particularly in an oceanic island tectonic setting.--Modified journal abstract.

Identification of chlorite and serpentine in cosmetic or pharmaceutical talc.

Chlorite is the most common accessory mineral group found in high purity talc ore used in cosmetic or pharmaceutical consumer talcum products. X-ray diffraction and wet chemical analytical data obtained on geologic samples representing commercial talc ore deposits of high purity and on processed samples representing talc found in consumer talcum products indicate that clinochlore and penninite are the two chlorite minerals most commonly found in all talc samples irrespective of origin or source, but sheridanite is also found in some samples representing talc deposits that are associated with serpentinite rocks. The chlorite minerals exhibit certain well-defined X-ray diffraction characteristics which differentiate them from each other as well as from those of serpentine minerals, including the hazardous chrysotile asbestos.

Expandable layer silicates associated with hydrothermal talc deposits of Murphy, North Carolina

Corrensite and other mixed-layer chlorites occur in the insoluble residues from the Murphy Marble. They are found in an ordered arrangement around one of the eight zones in the Murphy Marble. The envelope, 60 m wide, is centered on the mottled zone in the upper part of the marble formation. The progression of the layer silicates is: vermiculite --> vermiculite-smectite --> smectite --> smectite-chlorite --> corrensite + chlorite --> chlorite. In addition, quartz, plagioclase, and muscovite may occur. The mottled zone appears to have been a conduit of the hydrothermal fluids which have altered the silicates in the marbles; isotopic data supports this hypothesis. The altered carbonate rock is depleted in heavy isotopes. A genetic connection, between the talc bodies and the hydrothermal plumbing system, is indicated by an increase in the amount of expanding and contracting layers in the mixed-layer minerals of the mottled zone near the orebody.--Modified journal abstract.

Mineralogy of residual soils overlying a talc deposit

The residual soil overlying a talc deposit, which occurs as a lens between gneiss and serpentinite in Lancaster County, Pennsylvania, contains talc in all size fractions studied (10 μm to less than 2 μm) and in unfractionated samples. A study of soil samples, obtained by auger drilling, indicates that small amounts of talc can be detected by X-ray diffraction in samples obtained over a large area when the X-ray samples are prepared so that the clays are well oriented. Randomly oriented X-ray samples, in which the level of detection of talc is much poorer, also were successfully used to determine the presence of the talc body by means of quantitative measurements. In addition, the latter procedure was found to be superior in determining the actual size and location of the ore body. It is proposed that such procedures might be used in exploration for similar talc deposits.

Geologic and metallogenetic patterns in the Archean and Early Proterozoic of Bahia State, Eastern Brazil

The territory of Bahia State is part of the Sao Francisco structural province. The basement of the province is characterized by granite-greenstone and high grade metamorphic terrains developed during the Archean and Early Proterozoic. The Early Archean is represented by small tonalitic-granodioritic and enderbitic-charuockitic nuclei 3,500 Ma old. Several portions of gneissic-migmatitic and granulitie terrains have ages of 3,000 Ma and Rb/Sr isochronic values of 2,700 Ma that represent the principal phase of the Jequie geotectonic cycle. During the Early Proterozoic, extensive areas of the basement of the Sao Francisco province underwent intensive remobilization, through granitization and K-metasomatism related to the Transamazonico geotectonic cycle (2,200-1,800 Ma). Besides greenstone belts the granite-greenstcne terrains contain volcano-sedimentary (greenstone belt like) and platform sequences developed since the Archean to the Early Proterozoic. The high grade metamorphic terrains contain remnants of supracrustal sequences and basic-ultrabasic complexes. The metallogenic Framework of Bahia shows that more important mineral deposits such as Au, Cr , Cu, Fe-Ti-V, Pb-Zn-Mn, magnesite and tale are related to Archean and Early Proterozoic evolution. Gold deposits are located in volcanic rocks of greenstone belt environments, and in conglomerates of Witwatersrand type. Economic deposits of Cr, Cu, Fe-Ti-V are associated with mafic-ultramafic complexes in high grade metamorphic terrains. Pb-Zn and Mn mineralizations occur in volcano-sedimentary (greenstone belt like) sequences and the platform sequences contain large deposits of magnesite and talc.

Talc retinopathy in primates. A model of ischemic retinopathy: I. Clinical studies.

Four rhesus monkeys received intravenous injections of talc twice weekly for 3 1/2 to ten months. Within one month, talc particles were visible in fine perifoveal retinal vessels in the posterior pole. Continued deposition of talc could then be seen after subsequent injections. Hemorrhages in the nerve fiber layer, cotton-wool patches, and whitish plaques in the choroid were visible ophthalmoscopically. Fluorescein angiography revealed precapillary arteriolar occlusions, capillary nonperfusion, an abnormal foveal avascular zone, and retinal vascular leakage. Vitreous fluorophotometric findings were abnormal in all five eyes tested, while electroretinograms were normal in two eyes with advanced talc retinopathy. Talc retinopathy in the primate is similar to ischemic retinopathies in humans, including human talc retinopathy, sickle cell retinopathy, and hypertensive retinopathy. Subsequent reports will describe the light microscopic and ultrastructural changes in these eyes using tracer studies with in these eyes using tracer studies with horseradish peroxidase.

Medial Medullary Syndrome in a Drug Abuser

A 28-year-old woman with a long history of drug abuse experienced flaccid quadriplegia and bilateral loss of posterior column sensation a few minutes after an intravenous (IV) injection of methylphenidate hydrochloride. Subsequently, spasticity developed and she showed minimal functional improvement during a period of several months. Necropsy performed 8 1/2 months later showed systemic granulomatosis due to talc and two ischemic infarctions, one involving both medial medullary areas and the other involving the left frontal lobe. Deposits of talc, presumably from a medication prepared for oral use, were demonstrated in the small vessels in the area of the medullary infarction. This case is unique in that the medial medullary syndrome was apparently caused by an embolus of talc following its IV administration.

67Gallium Scanning in Talc-Induced Pulmonary Granulomatosis

We describe a case of pulmonary granulomatosis in a user who habitually injected methylphenidate (Ritalin) intravenously; symptomatic and objective improvement occurred with corticosteroid therapy. A scan of the lungs using radioactive 67gallium showed an increased concentration of 67gallium throughout both lungs. There was a reduction in abnormal accumulation of 67gallium, improvement in the arterial oxygen pressure and the diffusing capacity for carbon monoxide, and a reduction in the infiltrate on the chest x-ray film two months after the institution of therapy. Before treatment the patient's symptoms and arterial deoxygenation increased despite the cessation of her drug abuse, thus raising the question of a self-perpetuating inflammatory process in a case of pulmonary deposition of talc.

The mineralogy and origin of the talc deposits near Winterboro, Alabama

The north and south talc bodies near Winterboro, Alabama, are associated with Cambrian dolomite. The north body lies like a blanket in residual clay which overlies the dolomite bedrock, and the lense-shaped south body is oriented along a fracture in the dolomite with a strike of N 65 degrees W and a dip of 43 degrees NE. The nature and distribution of insoluble residues in the dolomite as well as textural and field evidence suggest that hydrothermal solutions and metasomatic processes produced talc in and near fractures in the dolomite. These solutions are apparently also responsible for the production of chlorite in the dolomite and in associated shales and sandstones, or chlorite metasomatites, beneath the south body. Weathering exposed the north body and part of the south body and produced brecciation and silicification as well as a residuum of talc and chlorite in the vicinity of the orebodies.Insoluble residues in dolomite obtained from diamond drill cores suggest that a mineralized halo of talc and chlorite extends at least 200 feet from the main orebody, with the talc to chlorite ratio increasing as the talc body is approached. This feature, the presence of talc in the residual soils overlying the dolomite, and the associated chlorite and chlorite metasomatites may be useful in prospecting for Winterboro-type talc deposits.

Talc deposits (mineral and ovarian) unearthed again: Gamble, J. F., Fellner, W. & Dimeo, M. J. (1979). An epidemiologic study of a talc workers. Am. Rev. resp. Dis.119, 741. Longo, D. L. & Young, R. C. (1979). Cosmetic talc and ovarian cancer. LancetII, 349

Talc deposits (mineral and ovarian) unearthed again: Gamble, J. F., Fellner, W. & Dimeo, M. J. (1979). An epidemiologic study of a talc workers. Am. Rev. resp. Dis.119, 741. Longo, D. L. & Young, R. C. (1979). Cosmetic talc and ovarian cancer. LancetII, 349