Gem-Quality Friedelite from the Kalahari Manganese Field Near Kuruman, South Africa

Abstract

T h e comparatively rare mineral friedelite was first reported in 1876 by Bertrand. This occurrence was in the manganese mine at Adervielle, in the Vallke du Luron of the Hautes Pyrenees, France. The mineral was named in honor of Charles Friedel, the French chemist and mineralogist. Since then, friedelite has been recorded as occurring sporadically in other manganese silicate deposits worldwide, including the Hartig mine near Pajsberg, Sweden (Lindstrom, 1891); the Sjo mine near Orebro, Sweden (Ingelstrom, 1891); the mines near Veitsch, Austria (Hoffmann and Slavik, 1909); the Buckwheat mine and Parker shaft, Franklin Furnace, Sussex County, New Jersey (Palache, 19 10); the Taylor mine, Franklin Furnace, and the mines at Sterling Hill, Sussex County, New Jersey (Palache, 1935); the Fe-Mn deposits at Dshumart and Kamya, Central Kazahkstan, U.S.S.R. (Kuyapova, 1960); and the deI posits of the Atasui region of Central Kazahlzstan (Kuyapova, 1968). It appears that only the occurrences at Franklin Furnace and Sterling Hill have produced gemquality friedelite (Sinkankas, 1959; Sinkankas, 1962; Arem, 1977; Webster, 1978). The suitability of this comparatively rare mineral for gem cutting has been mentioned by Sinkankas (1968)) Vargas (1969), and Vargas (1979). In November 1980, a little more than 100 years after its original discovery, a new occurrence of gem-quality friedelite was discovered, at the Kalahari manganese field in the Republic of South Africa. A brief description of the mineralization of this rare gem material and the circumstances that led to its discovery is presented here. MINERALIZATION The friedelite was found during shaft-sinking operations at the Middelplaats mine in the Kalahari manganese field, near Kuruman, northern Cape Province, Republic of South Africa (figure 1). It is associated with the lower manganese ore zone indicated in figure 2. The ore itself is a fine-grained mudstone into which the ore mineral, braunite, is incorporated in a highly disseminated state (Middelplaats Manganese Ltd., 1981). Koekemoer, a mineral dealer, relying on information supplied by the miners who removed the friedelite from the shaft, originally placed the occurrence in the upper portion of the 25-m-thick ore zone at a depth of about 395 m below the surface and a distance of about 75 m from the main shaft (personal communication, 1981). Subsequent follow-up investigations by Zaayman, the resident mine geologist, placed the friedelite locality at the base of the lower ore body near the old ventilation shaft. Unfortunately, the precise underground position could not be determined, inasmuch as that portion of the mine, once it was worked out, had been converted into maintenance workshops and all the rock faces covered by shotcrete, a cement aggregate applied at high pressure. Nevertheless, small fragments of friedelite were subsequently found in this vicinity (Zaayman, personal communication, 1982). On the basis of information received from the miners, it is estimated that originally two to three tons of low-grade manganese ore were collected, from which about 100 kg of friedelite (then thought to be a variety of rhodochrosite) and gan-