The Kuantan-Dungun area (6000 km 2) is an important tin district which produced about 40 % of all tin mined in the Eastern Granite Province of Peninsular Malaysia. It is the most important wolframite-producing district in Malaysia. The largest underground tin mine of Malaysia (Sungei Lembing) is also located in this area. The granitoids that occupy about 30% of the area have a Permian age (240 - 275 Ma) except for a Triassic stock at Paka near Dungun (220 Ma). The composition of the granitoids ranges from gabbro to biotite granite (monzogranite). The largest part is occupied by biotite granite which exhibits characteristics of both S-type granite derived from a sedimentary source rock and I-type granite derived from an igneous protolith. Hornblende-biotite granite (to granodiorite) and gabbro (to quartz diorite) are subordi nate. The basic to intermediate rocks have affinities to tholeiitic magma and are not genetically linked to the granites by fractional crystallization. But the gabbroic rocks and the granites may have had a co=on heat source. Only in hydrothermally altered portions, the Kuantan-Dungun granites show ele vated Sn concentrations (up to 34 ppm Sn). The tin concentrations in unaltered rocks are low (averaging 3 ppm Sn). The Kuantan-Dungun granites have in common with other granites in the Eastern Province, tin concentrations that seem to be unrelated to the dif ferentiation stage, i.e. tin is a decoupled element. Both the low tin concentrations and the decoupled behavior of tin are unusual features of granites associated with tin deposits. The metallogenesis of tin in the wolframite-cassiterite area of Kuantan-Dungun is different from that in cassiterite-dominated S-type granite systems with very subordinate wolframite in the Main Range, of which the BujangMelaka pluton in the Kinta Valley is a typical example. The Main Range batholith, in general , and the Bujang Melaka pluton, in particular, show a significant increase in tin concentration with increasing degree of magmatic differentiation, i.e. tin is much higher in late-stage differentiates than in less evolved rocks. But for the Kuantan-Dungun granites, the distribution coefficient of tin between melt and solid must have been near 1 during most of the crystallization history of the magma. Tin enrichment did not take place until the residual fluids separated from the crystallizing magma.
The Faleme iron district in the Kedougou-Kenieba inlier of the Paleoproterozoic Birimian Supergroup of West Africa consists of nine major and 19 minor orebodies, distributed in a belt 65 km long and 15 km wide. Two major exoskarn orebodies have total reserves of 320 million metric tons (Mt) magnetite ore with 42 percent Fe, and seven major supergene-enriched orebodies, which overlie endoskarn, have reserves of 310 Mt with 59 percent Fe. Previous workers advocated an (exhalative)-sedimentary origin for the primary ore. In this paper, however, we present strong evidence for contact-metasomatic skarn mineralization associated with microdiorite intrusions, with an emphasis on the Karakaene-Ndi and Goto deposits. The ore deposits of the Faleme district are the only major Precambrian magnetite skarn deposits worldwide that have not been subjected to postore metamorphism. The deposits of the Faleme district have many similarities to Phanerozoic magnetite skarn deposits that are associated with dioritic intrusions and also lack postore metamorphism. The endoskarn of the Karakaene-Ndi deposit is hosted by microdiorite with pervasive albitization. Garnet (And 56 –100 Grs 0 –43 Alm 0 –2 Sps 0 –1 Pyr 0 –1 ) and clinopyroxene (Di 58 –100 Hed 2 –42 ) are early phases. Individual grains of garnet and clinopyroxene commonly are inhomogeneous, with Fe being concentrated at the margin of the grains rather than in the core. Fe-rich zones in clinopyroxene are also enriched in Na. Biotite and magnetite precipitated relatively late, followed by pyrite (2 vol %) ± chalcopyrite ± pyrrhotite ± iss. Aqueous-carbonic fluid inclusions in quartz from one sample have CO 2 concentrations of 5 to 14 mol percent and indicate pressures of 300 to 900 bars and temperatures of 281° to 373°C at total homogenization. The magnesian exoskarn of the Goto deposit is hosted by dolomitic and calcitic marble, which locally contains graphite. Magnetite is associated with prograde clinopyroxene (Di 89 –100 Hed 0 –11 ) and phlogopite-rich biotite (Mg/(Mg + Fe)~0.89) as well as retrograde serpentine. Garnet is scarce. Sulfur concentrations average 1 wt percent. Pyrrhotite and subordinate pyrite ± chalcopyrite ± arsenopyrite ± pentlandite ± cobaltite postdate most of the magnetite. The exoskarn formed under more reducing conditions and at lower temperatures than the endoskarn. Magnetite in the exoskarn has trace element concentrations similar to those of magnetite in the endoskarn but is distinguished from igneous magnetite in granodiorite and magnetite in andesite (possibly of igneous origin) by low concentrations of Cr 2 O 3 and V 2 O 5 . Microdiorite is the most likely source of iron although no igneous magnetite in microdiorite could be identified. Microdiorite with only moderate hydrothermal alteration has lower iron concentrations (1.6–4.5% Fe 2 O 3(total) ) than unaltered granodiorite and weakly altered andesite in the area (avg ~7% Fe 2 O 3(total) ). Iron was probably leached from the moderately altered microdiorite and transferred into zones of intense alteration in microdiorite and host-rock marble. The low degree of hydrothermal alteration of granodiorite and small areal extent of andesite argue against a granodioritic or andesitic source of iron. The supergene ore is derived from endoskarn with about 30 percent Fe and consists of hematite and hydrous iron oxides. The largest orebodies have a thickness of 100 m and are located in the central part of hills that rise 250 m above the surrounding peneplain; the bottom of the enrichment zone usually is centered deep below the top of the hills. The absence of supergene enrichment in exoskarn orebodies probably is due to unfavorable structural conditions. Supergene enrichment of endoskarn was probably not exclusively by residual enrichment, in which Ca, Mg, Na, and Si were removed from the orebody, but also involved addition of Fe from descending solutions to the site of enrichment. Exploration for new supergene iron ore should be focused outside the exoskarn belt between Goto and Safa, as the deposits in this area are unlikely to have experienced major supergene enrichment. The Faleme district has some similarities to the geologic setting of iron oxide-copper-gold districts in which the deposits are hosted by dioritic rocks and may be representative of an iron oxide-rich end member of the iron oxide-copper-gold class. However, only about 3 t of gold have been mined from alluvial deposits in the area and the district is relatively poor in copper.
The strat-bound Ngwako Pan copper deposit is located in the northeastern part of the 250-km-long Neoproterozoic Ghanzi Ridge in northwestern Botswana. The sulfide mineralization occurs in the lowermost 25 m of the Middle Ghanzi Formation, which is composed of reduced facies (gray and greenish-gray) siliciclastic and subordinate carbonate metasediments. The 1- to 3.5-km-thick red-bed metasediments of the Lower Ghanzi Formation underlie the mineralized horizon. The distribution of copper ore in the Middle Ghanzi Formation shows a close spatial correlation with the occurrence of basaltic rocks in the Kgwebe Formation underlying the Lower Ghanzi Formation. The mineralized horizon is hosted by lacustrine or lagoonal sediments that were deposited on a paleohigh in a rift-related basin. The sediments were metamorphosed at lower greenschist facies conditions and tightly folded. The homogenization temperatures of fluid inclusions in secondary quartz are in the range of 57 degrees to 254 degrees C, the median being 179 degrees C. The major sulfide minerals, in order of decreasing abundance, are chalcocite- djurleite, bornite, chalcopyrite, pyrite, sphalerite, and galena. They occur as disseminations related to the intergranular porosity and permeability of the sediment and those related to fracture or shear porosity and permeability. Various load features indicate that at least part of the disseminated mineralization or its precursor sulfide minerals was deposited before major compaction was completed. Sulfurization of the sediment and possibly introduction of copper occurred early in the diagenetic history of the sediment. The mineralizing fluids were probably derived from oxidized ground water passing through red-bed footwall sediments. These fluids were enriched in copper where the aquifer was copper rich, i.e., where high Cu basaltic rocks constitute part of the source region of the siliciclastic sediments.
Zinc concentrates with a mercury content of >600 tons are processed by zinc smelters each year, with primary zinc producers contributing significantly to anthropogenic mercury emissions. The chief host of mercury in zinc concentrates is sphalerite, the mercury content of which varies depending on the type and age of the deposit. Sphalerites from Proterozoic exhalative deposits have high mercury concentrations; they were formed during periods when the mercury input via emanations from the mantle was high. Sphalerites from Phanerozoic exhalative and vein-type deposits have intermediate mercury concentrations; they probably received most of their mercury from fluid-rock interaction, with direct input of gaseous mercury from a mantle source being less important. Mississippi Valley-type deposits have low mercury concentrations; they probably formed from mineralizing solutions, the mercury content of which has been scavenged by organic phases.
The Nam Salu horizon at Kelapa Kampit on Belitung Island, Indonesia, is the richest stratabound tin mineralization in Southeast Asia. It belongs to a sequence of Carboniferous-Permian sediments and volcanics which have been intruded by granitoids of Triassic age. The Nam Salu horizon is a steeply dipping, 35-m-thick layer of stilpnomelane-chlorite-(biotite) phyllite which is exposed over a length of 3 km. The horizon carries high-grade cassiterite ore (1-2% Sn) 100 m along strike up to a height of 100 m. This orebody, which is being mined in the Nam Salu open pit, is located symmetrically on both sides of the Khoi-Wa fault which intersects the horizon at an angle of about 45 degrees .The horizon exhibits semicontinuous banding in the 0.2- to 15-mm range which is characteristically defined by its varying iron mineral content (magnetite, pyrrhotite, pyrite, ilmenite, and siderite), averaging 8 vol percent. Eutaxitic textures are preserved in one-third of the rock indicating its derivation from tuff.In the open pit, the horizon contains disseminations of abundant fine-grained (2-200-mu m) cassiterite which is randomly distributed in the felted phyllosilicate matrix. The banded rock is intersected by veinlets with an average thickness of 0.1 mm which postdate the disseminated cassiterite mineralization and constitute approximately 1 percent of the total rock volume. The early-phase veinlets are filled with pyrite, phyllosilicates, siderite, pyrrhotite, quartz, sphalerite, chalcopyrite, magnetite, arsenopyrite, sphene, and cassiterite (in order of decreasing frequency). Late-stage veinlets filled with galena, sphalerite, carbonates, fluorite, and bismuth minerals are subordinate.The Nam Salu open-pit orebody is characterized by high concentrations of Fe (avg 39.95% Fe 2 O 3 total Fe) which vary inversely with SiO 2 , Al 2 O 3 , TiO 2 , and Zr concentrations. The contents of CaO and NaO 2 are very low (avg 2 O (3.98%), Rb (1,270 ppm), and Cs (325 ppm) are high. The chemical composition corresponds to a mixture of iron-rich sediment (iron-formation) and basalt (texturally tuff) which has been altered by metasomatic processes. The hydrothermal fluids which interacted with the host rock produced a strong enrichment in some alkali metals by biotitization together with the introduction of Sn, Be, Bi, F, Nb, Pb, and W as well as a depletion in Na 2 O, CaO, and Sr. The hanging-wall and footwall rocks, which are composed of metasandstone, metasiltstone, and chert, have been much less reactive to hydrothermal fluids than the Nam Salu horizon and are distinguished by their low Sn and Rb concentrations.The alkali (Sn) metasomatism cannot be linked in time to the precipitation of the iron-rich sediment or the basaltic volcanism which deposited the water-laid tuff, since seawater had no or insignificant access to the operating hydrothermal system. This is evident from the high Rb and Cs concentrations as well as from the high ratios Rb/K (0.04) and Cs/K (0.01) in the Nam Salu horizon. The reaction with heated seawater would produce a depletion of Rb and Cs relative to K. Seawater has very low Rb/K and Cs/K ratios because Rb and Cs are preferentially removed from seawater through incorporation into marine sediments. Only residual fluids separating from a granite magma are known to produce rocks which have Rb and Cs concentrations as high as the Nam Salu horizon. The most likely source of the Sn-bearing fluids is granitic magmatism, though its nearest manifestations are the biotite granite outcrops 20 km to the east and 30 km to the west of Kelapa Kampit, respectively.
Highly radioactive, heat-producing waste contains radionuclides and generates daughter products that have half-lives as long as millions of years. This high-level waste must be sealed from the biosphere for a very long period in stable containers stored in deep geological repositories. Copper has been seriously considered as a container material in several waste-disposal projects. Native copper deposits may serve as natural analogues for a chemically stable container-repository system. These deposits formed in terrestrial basalt-conglomerate sequences at temperatures of approximately 100 to 200°C. The hydrothermal systems possessed oxygen fugacities below the stability limit of cuprite and at least 3 log units above the magnetite-hematite buffer at 100° C, and at least 1 log unit above this buffer at 200 ° C. This corresponds to an oxygen fugacity range of ≤10 log units. The fluids were characterized by low total sulfur activities and high Cu-Cl ratios. Similiar conditions can be expected to exist in a theoretical repository in subaerially extruded Cu-rich basalts interbedded with terrestrial conglomerates, which have undergone pervasive hydrothermal alteration.
