SAPPHIRE and GARNET from KALALANI, TANGA PROVINCE, TANZANIA by Antonin V

SAPPHIRE AND GARNET FROM KALALANI, TANGA PROVINCE, TANZANIA By Antonin V. Seifert and Jaroslav Hyrsl Located just 3 km south of the famous Umba he Kalalani area in northeastern Tanzania hosts sev- locality, the geologically similar Kalalani area eral primary deposits of sapphire and the largest pri- hosts deposits of gem-quality sapphire (red- mary deposit of pyrope-almandine in that country. In dish orange, yellow-brown, and other colors), T1989–1990, two significant discoveries of reddish orange pyrope-almandine, and tsavorite. The gems (“Umba padparadscha”; see figure 1) and yellow-brown sap- are mined principally from primary and elu- phires were made in desilicated pegmatites that cross-cut a vial sources associated with a serpentinite small serpentinite massif. In 1994, a primary deposit of tsa- body and surrounding metacalcareous rocks. The gemological properties of sapphires from vorite was discovered in the surrounding graphitic gneisses, Kalalani are very similar or identical to those and two pieces of gem-quality tanzanite were found in allu- from Umba. The garnets, however, are differ- vial sediments adjacent to the Kalalani serpentinite massif. ent: Tsavorite is not known from the Umba This article is based on field research by the senior area, and the dark red to brownish red pyrope- author, who acted as a consultant in the exploration and almandine from Kalalani is distinct from the mining of the sapphire deposits in 1989–1990, and also pink-purple rhodolite more commonly found mined the large pyrope-almandine deposit in 1994. The sec- at Umba. ond author visited the Kalalani area in 1993, and provided the laboratory data on the samples. LOCATION AND ACCESS The Kalalani gem deposits are located approximately 100 km northwest of the town of Tanga, and 6 km (or 14 km by dirt road) south of the Umba camp, at coordinates 4° 34’ S, 38° 44’ E (figure 2). This flat terrain is characterized by red- brown lateritic soil that is covered by thick bush vegetation and grasslands. The mining area, called “Vipigoni” by locals, ABOUT THE AUTHORS lies about 5 km northwest of Kalalani village, from where it Dr. Seifert ([email protected]) is a senior officer at can be accessed by a rough dirt road. During the rainy sea- the Czech Geological Survey, Klarov 3, Prague son (December–March), access to the area may be difficult. 1, Czech Republic. Dr. Hyrsl is a consulting mineralogist-gemologist based in Prague, and a former staff member of the Faculty of Natural GEOLOGY Sciences at Charles University in Prague. Regional Geology. The gem-bearing districts of both the Please see acknowledgments at the end of the Umba River and Kalalani areas are hosted by rocks of the article. Usagaran System, a part of the Mozambique Belt. These Gems & Gemology, Vol. 35, No. 2, pp. 108–120 rocks underwent several episodes of metamorphism, pluton- © 1999 Gemological Institute of America ism, thrusting, and folding during the Late Proterozoic to Early Paleozoic Pan-African orogenic event (Malisa and 108 Kalalani Sapphire and Garnet GEMS & GEMOLOGY Summer 1999 Figure 1. Most of the sapphires from the Kalalani area, which are typically fancy colors, have been mined from primary deposits. These reddish orange sapphires are from the Cham- Shama claim. The faceted stones range from 0.22 to 0.91 ct. Courtesy of Varujan Arslanyan, Arslan Jewelers, New York; photo © GIA and Tino Hammid. Muhongo, 1990). The area was geologically surveyed quite variable, since the pegmatites commonly by Hartley and Moore (1965) as part of the Quarter pinch and swell (see, e.g., figure 4). Like those at Degree Sheet 91 and 110, Daluni (scale 1:125,000). Umba (see Solesbury, 1967), the Kalalani pegmatites The rocks consist of high-grade banded gneisses of are generally coarse grained (up to 5 cm), and con- the granulite facies, gneisses of the amphibolite tain calcic plagioclase (andesine-labradorite) but no facies, graphitic gneisses, metacalcareous rocks, quartz. Other major constituents include amphi- quartzites, crystalline limestones, and meta-amphibole, vermiculite, chlorite, biotite, spinel, corun- bolites. These rocks surround two isolated bodies of dum, and kyanite (see, e.g., figure 5). serpentinite (i.e., the Umba and Kalalani serpentinite The mineralized zones of the two pegmatites massifs; see figures 2 and 3). The geologic setting, that yielded reddish orange and yellow-brown sap- mineral assemblages, and presence of gem-corun- phires measured approximately 6 m long and 2 m dum-bearing pegmatites at both localities suggest wide. Although these pegmatites were only about that these massifs have a similar geologic history. 50 m apart, they showed distinct differences. The reddish orange sapphire was mostly concentrated in Local Geology. Corundum Deposits. Gem-quality patches of clay minerals within “golden” yellow sapphire and ruby are confined to desilicated peg- vermiculite and was accompanied by pink spinel (of matites that cross-cut the serpentinite (figure 3). low cabochon quality) as an important indicator. They generally form lenticular (lens-like) bodies However, the yellow-brown sapphire was found that are oriented vertically, and measure about 5–10 within bluish green vermiculite, in the absence of m long and up to 2–3 m wide. The dimensions are clay, and the tracer mineral was spinel-pleonaste. Kalalani Sapphire and Garnet GEMS & GEMOLOGY Summer 1999 109 Ruby has been found at only two locations in Kalalani. At one of these, the senior author noted that tabular ruby was randomly distributed within biotite in a desilicated pegmatite, and was accompanied by crystals of color-change sapphire. Pyrope-Almandine Deposits. Along the eastern periphery of the Kalalani serpentinite are two areas Figure 2. The Kalalani gem deposits are associated with the Kalalani serpentinite massif in northeastern Tanzania (inset), a few kilometers south of the Umba area. Dirt tracks (shown here in brown) tra- verse both sides of the two serpentinite massifs between the villages of Umba and Kalalani. Figure 3. The Kalalani serpentinite is cross-cut by desilicated pegmatites that locally contain gem corundum. Pyrope-almandine is mined from meta- amphibolites near the boundary of the serpentinite, and tsavorite deposits are hosted by graphitic gneisses southwest of the serpentinite. The deposits are desig- nated here according to the name of their claim block: 1 = original “Papas” pit, reopened by Ruvu Gem Ltd. (color-change sapphire, ruby); 2 = Cham- Shama (reddish orange sapphire); 3 = Cham-Shama (yellow-brown sapphire); 4 = Peter A. (an old “Papas” pit; light blue and pink sapphires, ruby); 5 = Sumai (yellow-brown sapphire); 6 = old “Papas” pit, reopened by Africa-Asia Precious Stones and Mining Co. (light blue and yellow sapphires); 7 = Peter A. (pink sapphire); 8 = Cham-Shama (pink sapphire); 9 = Peter A. (pyrope-almandine/rhodolite); 10 = Salehe J. (pyrope- almandine) 11 = Abdalah (tsavorite, main pit); 12 = Ruvu Gem Ltd. (tsavorite); 13 = Maluki C. (tsavorite); and 14 = Kwendo N. (alluvial garnet, sapphire, and rare tanzanite). Mapped by A.V. Seifert, 1994. 110 Kalalani Sapphire and Garnet GEMS & GEMOLOGY Summer 1999 that contain meta-amphibolites (see figure 3). The southern amphibolite body hosted an economic deposit of pyrope-almandine (Peter A. claim), along the faulted and sheared contact with serpentinite (figure 6). The mineralized zone measures 100 m long, varies from 6 to 12 m wide, and dips 45° northwest. The pyrope-almandine occurred in nodules averaging 10 cm in diameter. The nodules were typically fractured masses that contained flat- tened pieces of pyrope-almandine embedded in a fine-grained yellowish dolomite (figure 7). The best- quality stones were recovered from the northeastern part of the deposit; the material from the south- Figure 5. At the Cham-Shama claim, reddish orange sapphire crystals were recovered from desil- western part was more fractured and was heavily icated pegmatites composed mainly of vermiculite included. (brown flakes), calcic plagioclase (white), and amphibole and chlorite (dark green). The prismatic Tsavorite Deposits. Graphitic gneisses near the sapphire crystal in the center of the photo is about southwestern part of the serpentinite body are 4 cm long. Photo by Varujan Arslanyan. interbedded with quartz lenses that are accompanied by accumulations of pure graphite, where tsavorite has formed locally. These lenses crop out locally over a distance of about 1.7 km, and each is elongated up to 25 m in a southeasterly direction; Figure 4. This geologic map (top) and cross-section they vary in width from a few centimeters up to 2 (bottom) of the Cham-Shama reddish orange sap- m. At least four parallel zones showing surface phire deposit show the sapphire-bearing desilicat- signs of tsavorite mineralization were traced in this ed pegmatite and associated veins. Abbreviations: area. a = desilicated pegmatite containing patches of clay minerals (white) with sapphire; b = blue- green vermiculite vein; c = golden yellow vermiculite vein; d = pyroxenite vein. Mapped by A.V. Figure 6. This geologic cross-section shows the Seifert, 1990. northeastern part of the Peter A. pyrope-almandine deposit. The garnet is found as fractured nodules within altered lenses of meta-amphibolite. The mineralized meta-amphibolites have been faulted and sheared within the serpentinite. Mapped by A.V. Seifert, 1994. Kalalani Sapphire and Garnet GEMS & GEMOLOGY Summer 1999 111 who developed three shallow open pits to explore the pegmatites in the 1960s. Since then, the Kalalani area has been worked continuously by local miners who hand sieve the eluvial soil cover in search of fancy-color sapphires and ruby. Organized mining of primary deposits virtually ceased from the 1970s into the early 1980s, when the original “Papas” pit, situated on the eastern bor- der of the serpentinite (figure 3, location 1), was reopened by Ruvu Gem Ltd. At 40 m, this is now the deepest mine in the Kalalani area.

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