Tungsten exploration in semiarid environment: Central Anatolian massif, Turkey

Journal of GeochemicaIExploration, 31 (1989) 185-199

185

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Tungsten exploration in semiarid environment: Central Anatolian massif, Turkey AKIF OZCAN' and M. NAMIK (~AGATAY2

1Turkish Glassworks, Topkapi, Istanbul, Turkey 2King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia (Received February 18, 1988, revised and accepted June 14, 1988)

ABSTRACT

Ozcan, A. and ~agatay, M.N., 1989. Tungsten exploration in semiarid environment: Central Anatolian massif, Turkey. J. Geochem. Explor., 31: 185-199. Regional and detailed heavy-mineral surveys were carried out in the western part of the Central Anatolian massif which is composed mainly of pre-Mesozoic greenschist metamorphic series intruded by Paleocene granitic intrusives. The region is characterized by moderate relief and a semiarid climate. The regional heavy-mineral survey, covering an area of 2000 km 2 with a sample density of about 1 sample per 10 km 2, involved concentration of heavy minerals by panning and analysis of half the sample for W and Sn after grinding to -75/~m. The remaining half was mineralogically analyzed using microscopic techniques. The results of the regional survey show that anomalous W and Sn values are spatially related to granitic intrusions and their contacts with metamorphic basement rocks. Detailed heavy-mineral surveys and geologic mapping in the Yagmurlu-Karincali area - the most distinct W anomalies delineated by the regional survey - indicate that the scheelite-bearing mineralized zones are associated with intensive silicification and quartz veins in the metamorphic series. Chemical and mineralogical analyses of the different size fractions of the heavy-mineral concentrates demonstrate that scheelite is concentrated in the coarse fractions ( > 180/Ira). However, the -180/zm fraction data provides less erratic dispersion patterns. A geochemical stream sediment survey in the Yagmurlu-Karincali area, involving the chemical analysis of - 1 8 0 / m l fraction for W, Mo, Cu, Pb, and Zn, failed to produce any anomalies related to the scheelite mineralization outlined by the heavy-mineral surveys. Tungsten showed only a weak anomaly in the Yagmurlu area. Chemical and mineralogical analyses of the heavy-mineral concentrates of soils were able to outline the scheelite source effectively. However, the dispersion patterns are narrow. The drainage. sediments show enrichment of scheelite relative to the associated soils. Among all the elements analyzed o ~ y As appears to be a good pathfinder for scheelite mineralizations in this region.

INTRODUCTION Heavy-mineral analysis has been used successfully in mineral exploration i n m a n y p a r t s o f t h e w o r l d f o r A u , P t , S n , T i , C r , W , T1, r a r e - e a r t h e l e m e n t s ,

0375-6742/89/$03.50

© 1989 Elsevier Science Publishers B.V.

186

base metal sulfides and diamond (Theobald and Thompson, 1959; Zeschke, 1961; Overstreet, 1963; Bell, 1976; Gleeson and Boyle, 1980). In addition to their use in mineral exploration, heavy-mineral surveys provide invaluable data on the geology of surveyed area. During 1979-1981, regional and detailed heavy-mineral surveys were carried out in the Kaman-Kirsehir sector of the Central Anatolian Massif as part of a large mineral exploration program under the auspices of the Mineral Research and Exploration General Directorate of Turkey (MTA). Widespread occurrence of various compositional types of Paleocene granites and their favourable contact zones make the region an important exploration target for many metals. The region is characterized by a moderate relief and a semiarid climate. Some perennial streams are present, but most streams are dry during the summer season. Soils in the area are immature residual soils, having a thickness of up to 30 cm. A regional heavy-mineral survey, involving chemical and mineralogical analyses of various fractions from stream sediments, was carried out. The survey revealed the presence of two W anomalies close to the villages of Karincali and Yagmurlu (Fig. 1 ). Detailed heavy-mineral follow-up surveys and geologic mapping of the Karincali-Yagmurlu area subsequently revealed the presence of scheelite mineralization associated with quartz veins within the silicified metamorphic rocks. GEOLOGY AND MINERALIZATION

The study area covers a large part of the Central Anatolian Massif which is composed of four groups of lithological units, namely a pre-Mesozoic metamorphic series, a Jurassic to Upper Cretaceous ophiolitic Ankara Melange, Paleocene granitic intrusives, and Tertiary sedimentary cover rocks (Fig. 1 ). In the study area the metamorphic series has a highly variable lithology, consisting of mica schist, mica-quartz-feldspar schist, calc-schist, marble with bands of chlorite- and calc-schist, and quartzite. The grade of metamorphism of these rocks over the massif varies from greenschist to amphibolite facies (Erkan, 1976; Seymen, 1981). The ophiolitic rocks of the Ankara Melange overlie the metamorphic basement with a tectonic contact and consist of limestone, marl, radiolarite, shale, graywacke, pillow lava, serpentinite, and blocks of crystalline limestone showing a state of tector, ic chaos in the west (Norman, 1972; Seymen, 1981). The intrusive igneous rocks of Paleocene age (Ayan, 1963 and Ataman, 1972 ) intrude both the metamorphic series and the ophiolitic rocks. Their composition is variable, belonging to the calc-alkaline and alkaline series. These intrusions have produced contact metamorphic effects along their borders with calcareous rocks, forming skarns of variable mineralogy. The sedimentary rock units cover large areas of the study region. The prin-

187

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cipal members include the Lower Eocene flysch, Lutetian volcanic-sedimentary series, Oligo-Miocene evaporitic series and the Pliocene unconsolidated sediments (Ketin, 1963; Oktay, 1981). Most of the mineral occurrences in the region are associated with the Paleocene intrusions. These include Fe (Oztiirk, 1978), argentiferous Pb (~avu~o~lu, 1966), skarn-type W and Mo deposits (Ketin, 1963), Mo mineralization located in pegmatites within the granodiorites (Nadir and Olsner, 1936) and fluorite veins and U anomalies (Friedrich, 1960) related to the syenitic intrusions. The location of the known mineralization in the region is shown in Fig. 1. In the Yagmurlu-Karincali tungsten area, discovered as a result ofthe present investigation, the oldest rocks belong to the Kalkanlidag Formation which consists of mica schists grading upwards into calcareous schist {Fig. 2 ). Milky quartz bands, a few centimetres thick, are abundant within this formation, and

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189 thick quartzite lenses are also occasionally present. The Kalkanlidag Formation is conformably overlain by the Tamadag Formation, which consists of marble and calc-schistwith chlorite-schistbands in the lower units and quartz schist and quartzite in the upper units. These rocks are laminated and foliated with a m a x i m u m thickness of about 200 m. The metamorphic succession is unconformably overlain by unconsolidated gravels and sands of the Pliocene Kizilirmak Formation (Oktay, 1981). The metamorphic rocks are highly silicifiedalong faults and fractures;sericitizationis also common. These silicifiedzones are a few k m long, steeply dipping, and include milky quartz veins with thicknesses ranging from about 10 c m to 10 m (Fig. 2). Scheelite mineralization occurs mainly along the contact zones of the quartz veins with marble and calc-schist.The mineralized zones contain pyrite, pyrrhotite, arsenopyrite, and occasionally chalcopyrite or magnetite, in addition to scheelite as the main ore mineral. The scheelite has an average grain size of about 0.15 m m and a m a x i m u m sizeof I ram. The grade of the mineralized zones is highly variable from a few tens ofppm to 5 % WO3. Pyritization,devoid of scheelite,is often associated with aplitedykes. MATERIALS A N D M E T H O D S

Sample collection and preparation Drainage sediments consisting of 5 litersof the -5 m m fraction were collected to give sample densities of about I sample per 10 k m 2 and I sample per k m 2 for the regional and detailedsurveys, respectively.Care was taken to sample consistently from low-energy locations for a satisfactorysubsample (Day and Fletcher, 1986). The heavy-mineral fractionof 180 samples collectedduring the regional survey were concentrated by panning. After removal of magnetite, half of the concentrate was ground to -75 ~ m to reduce subsampling variation during chemical analysis (Harris, 1982; Saxby and Fletcher, 1986). The other half was subjected to mineralogical analyses. The panned concentratesof 27 samples from the Karincali and Yagmurlu areas were sieved through I m m and 180/~m sieves and the -1000 + 180/~m and -180 # m fractionswere used for chemical and mineralogical analyses. Five-litersamples were collectedfrom the top 10 cm of the soilprofile,along the slope from known scheelite-bearingzones in the Karincali and Yagmurlu areas. Three composite samples, each covering a channel length of 25 m across the traverse were collected at each location,with the down-slope sample separation varying from 25 to 150 m. The samples were panned and then sieved through 1000, 330 and 180/~m sieves. The -1000 + 330/~m and -330 + 180/tm fractions were further concentrated by separation with tetrabromoethane (SG: 2.95). The two fractions were chemically and mineralogically analyzed. For the conventional stream sediment geochemical survey, covering the area

190 around and south of Karincali and Yagmurlu, a sampling density of about 1 sample per km 2 was used with the -180 #m fraction of a 500-g sample being chemically analyzed.

Mineralogical analysis Heavy-mineral compositions of samples were determined by binocular, petrographic and ore microscopy. Scheelite contents were estimated by grain counting under ultraviolet (UV) light and refer to to the number of scheelite grains in 2.5 liters Of soils or drainage sediment.

Chemical analysis Analysis of W, Sn and As in stream sediment and heavy-mineral samples were carried out using colorimetric procedures. The Zn-dithiol method was used for the determination of W after carbonate-nitrate fusion (Stanton, 1966). Tin was analyzed colorimetrically after an ammonium iodide fusion-sublimation (Stanton, 1966). The detection limit of both methods is 4 ppm W or Sn and the precision is _+20% at the two standard deviation level. Arsenic was analyzed using the Gutzeit method (Stanton, 1966). This method has a detection limit of 2 ppm and precision of + 20% at the two standard deviation level. The element concentrations of heavy-mineral fractions are based on the total weight of each of those fractions. This method of presentation has been shown by Saxby and Fletcher (1986) to reduce hydraulic effects as a source of noise in heavy-mineral sampling. Copper, Pb and Zn were analyzed by atomic absorption spectroscopy using an air + acetylene flame after a hot nitric acid digestion. The precision of the method for these elements is better than _+20% at the two standard deviation level. RESULTS AND DISCUSSION

Regional heavy-mineral and stream sediment surveys The W and Sn contents for heavy-mineral concentrates of the regional survey approximate to lognormal distributions. The W data give a trimodal population, with the first mode corresponding to values less than 4 ppm and comprising 72% of the population. The rest of the data exhibit a bimodal distribution with an inflection point at 60 ppm W. The Sn data show a bimodal distribution. The W and Sn populations were partioned and the class intervals for data plotting were selected according to the procedures outlined by Sinclair (1976). Tin and W in the heavy-mineral concentrates display anomalous values spa-

191

Fig. 3. Tungsten content of heavy-mineral concentrates of drainage sediments for the regional survey. Framed area in the southeast corner outlines the conventional drainage survey area shown in Figs. 5 and 6. tially related to granitic intrusions and their contacts with metamorphic basement rocks (Figs. 3 and 4).The intermediate strength Sn anomaly in the Ophiolitic Series south of the region is most likely related to small granitic intrusions cross-cutting the ophiolites. The most significant and persistent anomalies appear to be the two W anomalies located around the Karincali and Yagmurlu villages, west of Kirsehir. The high W contents, together with hydrothermal alteration effects in the metamorphics, make this area highly favourable for economic mineralization. These anomalies were, therefore, chosen for detailed follow-up studies. The W distribution obtained for the conventional stream survey exhibits a single anomaly in the Karincali area (Fig. 5 ). Most of the W values are at or below 4 ppm and the maximum W value is 15 ppm. The Zn distribution shows a well-defined anomaly north of the Yagmurlu W anomaly (Fig. 6). Copper

192

Fig. 4. Tin content of heavy-mineral concentrates of drainage sediments for the regional survey.

shows a similar distribution to that of Zn. Peak values of Zn and Cu are 200 and 84 ppm, respectively. Lead and Mo patterns did not yield any clear anomalies. Field studies revealed that the Cu-Zn anomaly is related to the predominance of chlorite schist in this part of the area. Considering that the Cu-Zn anomaly is not directly related to W mineralization and the weak nature of the W anomaly, the heavy-mineral drainage surveys can be considered to be superior to the conventional drainage sediment surveys in this region. Heavy-mineral surveys in the Yagmurlu and Karincali areas

Based on the results of the regional survey, detailed heavy-mineral surveys involving drainage sediments and soils were carried out in the Yagmurlu and Karincali anomaly areas. The heavy-mineral sampling was accompanied by 1/ 25,000 scale geologic mapping and UV light examination in the field at night time.

193

Fig. 5. Tungsten content of -180/~m drainage sediment fraction in the Yagmurlu-Karincali area.

Stream sediments. The -1000 ÷ 180 #m and -180 z m fractions of heavy mineral concentrates of the drainage sediments were chemically analysed for W, Cu, Pb, and Zn. Tungsten generally exhibits the highest concentration in the coarse (-1000 ÷ 180 #m) fraction (Table 1). However, its distribution in this fraction is more erratic than the -180 ~m fraction. Tungsten contents of the two heavy mineral size fractions in the Karincali area (Fig. 7) also suggest higher but more erratic concentrations of W in the coarser fraction than in the finer fraction. Tungsten values often increase downstream from mineralized zones (Fig. 7); a feature due to heavy-mineral concentration by gradual winnowing (i.e. removal) of the light minerals along the stream as stream velocity increases (Sirinawin et al., 1987). The statistical distribution parameters (Table 1) and correlation matrix (Table 2), as well as the spatial distribution of Cu, Pb and Zn, suggest no plausible relationship with the scheelite mineralization. Tungsten shows a strongly positively-skewed distribution (approximating to a lognormal distribution) as evidenced from the large disparites between its average, mode and geometric mean whereas the same parameters for the other elements are close

194

Fig. 6. Zinc content of -180 pm drainage sediment fraction in the Yagmurlu-Karincali area.

to each other (Table 1 ). This difference between the W and base metal populations arise from the differences in their mobilities and mode of dispersion with W showing low mobility and having a predominantly clastic type of dispersion. Variations in Cu, Pb and Zn data can be accounted for mainly by aplite-associated pyrite mineralization in the Karincali area and, mafic lithology (mainly chlorite schist) in the Yagmurlu area. Scheelite grain counts of stream sediment concentrates (-1000/2m fraction) from the Yagmurlu area were undertaken by binocular microscope inspection using UV light illumination. The scheelite counts for 78 concentrates give a bimodal distribution with an inflection point at the 20th percentile corresponding to 60 scheelite grains. The areal distribution of scheelite counts clearly shows the association of high counts with mineralized quartz veins in the silicified southern zone of the area (Fig. 8). The mineralogical anomalies appear to persist for a length of at least 3 km from mineralization. Some intermediate scheelite counts north of Yagmurlu are due to smaller-scale mineralized zones associated with silicification. The distribution of scheelite counts shows good

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TABLE 1 Basic statistical parameters for W, Cu, Pb and Zn in the two size fractions of the heavy mineral concentrates of Yagraurlu-Karincali stream sediments (27 samples; values in ppm). Statistical parameter Average Median Mode Geom. mean Minimum Maximum

-1 ram+ 180/~m fraction

-180/ma fraction

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Zn

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1Values not included in calculation of the average.

agreement with the W distribution obtained in this area during the regional heavy-mineral survey (Fig. 3). The following minerals were identified in polished thin sections of stream sediment concentrates from the Yagmurlu and Karincali areas: scheelite, partially oxidized pyrite and pyrrhotite, arsenopyrite, magnetite, hematite, limonite, sphene, rutile, titanite, chromite, pyrolusite and psilomelane. Scheelite and

196

TABLE

2

Pearson correlation matrix of heavy-mineral geochemical data for the two size fractions of heavymineral concentrates from the Yagmurlu-Karincali stream sediments (27 samples ). Significant values at 95% confidence level are italicized. -1 m m + 180/~m fraction

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Zn

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197

arsenopyrite have been exclusively derived from the scheelite-bearing quartz veins, whereas pyrite and pyrrhotite and their alteration product, limonite, have been weathered from the quartz veins, silicified zones and aplites. Soils. Composite soil samples were collected along slope traverses crossing the richest W zone to the east ofBoz Tepe in the Karincali area (Fig. 9) and the quartz veins in the Yagmurlu area. The mineralogical and chemical analyses of the heavy-mineral concentrates from the soils show very close agreement {Fig. 9). The W content of the -350 + 180 pm fraction, and the scheelite counts of the -1000 +350/~m and -350 +180 #In fractions show a sharp anomaly directly above mineralization which levels off down slope and increases again in the sample collected near the head of the stream. High values in this last sample suggest the effectiveness of the surface runoff process in concentrating heavy minerals at the base of the slope. The good agreement between the mineralogical and chemical method of analyses is also illustrated by the strong correlation coefficients ( > 0.93) found between the scheelite counts and W values. Arsenic shows high concentrations (up to 1200 ppm) and a wide distribution in soils surrounding the scheelite-bearing quartz vein. Considering the association of arsenopyrite with the scheelite mineralization and its wide dispersion, arsenic appears to be a good pathfinder for W in this region. Weights of the heavy-mineral concentrates of the various soil size fractions expressed as a percentage of the total heavy-mineral content give ranges of 38(X100)12

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198

58%, 32-48%, and 4-28% in t h e - 1 0 0 0 + 3 3 0 / t m , - 3 3 0 + 180/~m, a n d - 1 8 0 #m fractions, respectively. The variations in the weight of the heavy minerals appear to be unrelated to W contents and scheelite counts in these size fractions. CONCLUSIONS

A regional heavy-mineral survey conducted in the Kaman-Kirsehir sector of the Central Anatolian massif delineated a number of tungsten anomalies. Follow-up drainage heavy-mineral surveys and geological mapping in the Yagmurlu and Karincali areas - the most important W anomalies outlined by the regional survey - showed that the W (scheelite) mineralization is associated with intensively silicified zones and quartz veins. The radial arrangement of these mineralized zones (Fig. 2) and the widespread occurrence of aplites suggest the possible presence of a granite cupola under the metamorphics as proposed in genetic models for tungsten deposits by Kelly and Rye (1979) and Noble et al. (1984). A comparison of heavy-mineral and conventional drainage surveys shows the superiority of the former in this environment. In drainage sediment concentrates W exhibits lower levels but less erratic variation in the -180 /tm fraction than the -1000 + 180/~m fraction. Chemical and mineralogical analyses of heavy concentrates from two soil profiles delineate the source effectively, with narrow well-defined anomalies that level off sharply down the slope from the source. The drainage sediments show enrichment of scheelite relative to the associated soils, a result of heavy-mineral concentration by winnowing {removal) of light minerals by the streams. The dispersion patterns of Cu, Pb and Zn do not appear to be related to scheelite mineralization. This study demonstrates the effectiveness of mineralogical and chemical analyses of drainage sediment and soil concentrates in detecting anomalous patterns at various scales in a semiarid environment. The results suggest that for low "noise", smooth analytical data and improved contrast, special attention should be paid to selection of the right grain size. ACKNOWLEDGEMENTS

The authors wish to thank General Directorate of Mineral Research and Exploration (MTA), Turkey for the field and laboratory support, and permission to publish this paper. Critical reading of the manuscript by Dr. D.R. Boyle of Geological Survey of Canada is gratefully appreciated. REFERENCES Ataman, G., 1972. Preliminary radiometric age of the Cefalik Dag granite-granodioritic massif, southeast of Ankara. Hacettepe Fen Muhendislik Bilimleri Dergisi, 2:44-49 (in Turkish). Ayan, M., 1963. Contribution h l'~tude p6trographique et g~ologique de la r~gion situ~e au nordouest de Kaman. Maden Tetkik Arama (MTA) Publ. 115, 332 pp.

199

Bell, H., 1976. Geochemical reconnaissance using heavy minerals from small streams in central South Carolina. U.S. Geol. Surv., Bull. 1404, 23 pp. ~avu}oglu, H., 1966. Geology of Keskin-Denek Pb-Zn mineralization, Maden Tetkik Arama Enst. Rep. No. 3871, Ankara (unpubl., in Turkish). Day, S. and Fletcher, K., 1986. Particle size and abundance of gold in selected stream sediments, southern British Columbia, Canada. J. Geochem. Explor., 26: 203-214. Erkan, Y., 1976. Determined isograds of regional metamorphism around Kirsehir and their petrologic interpretation. Hacettepe Univ. Yerbilimleri Dergisi, 2:23-54 (in Turkish). Friedrich, K.M.G., 1960. Detailed radiometric prospection of mineral deposits in Keskin. Maden Tetkik Arama Enst. Rep. No. 3150, Ankara (unpublished). Gleeson, C.F. and Boyle, R.W., 1980. Minor and trace element distribution in the heavy minerals of the rivers and streams of the Keno Hill district, Yukon Territory. Geol. Surv. Can. Pap., 7631: 1-9. Harris, J.F., 1982. Sampling and analytical requirements for effective use of geochemistry in exploration for gold. In: A.A. Levinson (Editor), Precious Metals in the Northern Cordillera. Assoc. Explor. Geochem. Rexdale, Ont., pp. 53-67. Kelly, W.C. and Rye, R.O., 1979. Geologic, fluid inclusion and stable isotope studies of the tintungsten deposits of Panasquiera, Portugal. Econ. Geol., 74: 1721-1822. Ketin, I., 1963.1/500,000 scale geologic map of Turkey-Kayseri sheet. Made Tetkik Arama Enst. Educat. Ser. 16. Nadir, A. and Olsner, C., 1936. The Keskin-Denek Dagi molybdenum mineralization. Maden Tetkik Arama Enst. Rep. No. 630, Ankara (unpubl., in Turkish). Noble, S.R., Spooner, E.T.C. and Harris, F.R., 1984. The Logtung large tonnage, low-grade W (scheelite) - Mo porphyry deposits, south-central Yukon Territory. Econ. Geol., 79: 848-868. Norman, T., 1972. Stratigraphy of the Upper Cretaceous-Lower Tertiary sequence in the AnkaraHahsihan region. Bull. Geol. Soc. Turk., 15: 180-276. Oktay, F.Y., 1981. Geology and Sedimentology of the sedimentary cover of the Central Anatolian massif in the Savcilibuyukoba (Kaman) area. Thesis, Istanbul Technical Univ., 175 pp. (unpubl., in Turkish). Overstreet, W.C., 1963. Regional heavy-mineral reconnaissance as a guide to ore deposits in areas underlain by deeply weathered crystalline rocks. In: Proceedings of the seminar on geochemical prospecting methods and techniques (Bangkok, August 5-14, 1963), U.N. Mineral Res. Dev. Set., 21: 57-66. Oztiirk, M., 1978. Detailed geologic report on the Durmuslu-Kaman-Kirsehir iron mineralization. Maden Tetkik Arama Enst. Rep. No. M-333, Ankara (unpubl., in Turkish). Saxby, D. and Fletcher, K., 1986. The geometric mean concentration ratio as an estimator of hydraulic effects in geochemical data for elements dispersed as heavy minerals. J. Geochem. Explor., 26: 223-230. Seymen, I., 1981. Stratigraphy and metamorphism of the Kirsehir massif around Kaman (Kirsehir, Turkey). Bull. Geol. Soc. Turk., 24 (2): 7-14 (in Turkish with English abstract). Sinclair, A.J., 1976. Application of Probability Graphs in Mineral Exploration. Assoc. Explor. Geochem., Spec. Vol. 4, Rexdale, Ont., 95 pp. Sirinawin, T., Fletcher, W.K. and Dousset, P.E., 1987. Evaluation of geochemical methods in exploration for primary tin deposits: Batu Gajah-Tanjong Tualang area, Perak, Malaysia. In: R.G. Garrett (Editor), Geochemical Exploration 1985. J. Geochem. Explor.,, 29: 165-181. Stanton, R.E., 1966. Rapid Methods of Trace Analysis for Geochemical Applications. Edward Arnold (publishers) Ltd. London, 96 pp. Theobold, P.K. and Thompson, C.E., 1959. Geochemical prospecting with heavy mineral concentrates used to locate a tungsten deposit. U.S. Geol. Surv., Circ. 411, 13 pp. Zeschke, G., 1961. Prospecting for ore deposits by panning heavy-minerals from river sands. Econ. Geol., 4: 1250-1257.