Kombat Mine Research Articles

Connoisseur's Choice: Nambulite, Kombat Mine, Grootfontein, Otjozondjupa Region, Namibia

The discovery of nambulite at the Kombat mine in Namibia in 1975 raised the bar for this rare species. Originally described three years earlier from the type locality in Japan, Kombat was the secon...

Re-Evaluation of Kombat-Style Mineralization and Implications for Exploration in the Otavi Mountainland, Namibia

This study re-evaluates the characteristics of Cu-Pb-Ag and Fe-Mn ore mineralization of the Kombat Mine and Gross Otavi Mine based on field geology, fluid inclusions, petrology, mineralogy, and geochemistry. This is to determine the genetic relationship between Fe-Mn and Cu-Pb-Ag mineralization. The study has established that the Cu-Pb-Ag ore at the Kombat Mine can be classified as a variant of MVT-type deposit, whereas the Fe-Mn ore can be classified as a stratiform-syn-sedimentary deposit. The formation of the MVT-type deposit is associated with a hydrothermal fluid system with a mean temperature of 183°C and mean salinity of 12.85 wt. % NaCl equivalent. The syn-sedimentary Fe-Mn ore, which is largely associated with calc-silicate lithologies, consists mainly of magnetite and hematite with minor pyrite, hausmannite and jacobsite, and was deposited by diagenetic and mixed diagenetic-hydrogenetic processes under changing oxic and anoxic conditions within the sedimentary basin. Acceptable geochemical exploration indicators of the existing mineralization include anomalous values above 0.5% Cu, 0.2% S; 0.05% Pb; 0.04% As; 0.01% Zn; V, W, Mo, and Ag are 0.002%. Mineralogical indicators include chalcopyrite, bornite, covellite and galena with minor chalcocite, sphalerite, and tennantite for the Cu-Pb MVT-type ores at Kombat Mine.

Erikjonssonite, (Pb32O21)[(V,Si,Mo,As)O4]4Cl9, a new mineral from the Kombat mine and structural classification of layered lead oxychlorides related to litharge

Erikjonssonite, (Pb32O21)[(V,Si,Mo,As)O4]4Cl9, a new mineral from the Kombat mine and structural classification of layered lead oxychlorides related to litharge

Grootfonteinite, Pb3O(CO3)2, a new mineral species from the Kombat Mine, Namibia, merotypically related to hydrocerussite

Grootfonteinite, Pb3O(CO3)(2), is a new Pb oxycarbonate found in a mineralogically complex, banded assemblage from the Mn (-Fe) oxide ore unit of the Kombat mine. Grootfonteinite is named after the ...

Roymillerite, Pb24Mg9(Si9AlO28)(SiO4)(BO3)(CO3)10(OH)14O4, a new mineral: mineralogical characterization and crystal chemistry

The new mineral roymillerite Pb24Mg9(Si9AlO28)(SiO4)(BO3)(CO3)10(OH)14O4, related to britvinite and molybdophyllite, was discovered in a Pb-rich assemblage from the Kombat Mine, Grootfontein district, Otjozondjupa region, Namibia, which includes also jacobsite, cerussite, hausmannite, sahlinite, rhodochrosite, barite, grootfonteinite, Mn–Fe oxides, and melanotekite. Roymillerite forms platy single-crystal grains up to 1.5 mm across and up to 0.3 mm thick. The new mineral is transparent, colorless to light pink, with a strong vitreous lustre. Cleavage is perfect on (001). Density calculated using the empirical formula is equal to 5.973 g/cm3. Roymillerite is optically biaxial, negative, α = 1.86(1), β ≈ γ = 1.94(1), 2V (meas.) = 5(5)°. The IR spectrum shows the presence of britvinite-type tetrahedral sheets, $${\text{CO}}_{3}^{2 - }$$ , $${\text{BO}}_{3}^{3 - }$$ , and OH− groups. The chemical composition is (wt%; electron microprobe, H2O and CO2 determined by gas chromatography, the content of B2O3 derived from structural data): MgO 4.93, MnO 1.24, FeO 0.95, PbO 75.38, B2O3 0.50, Al2O3 0.74, CO2 5.83, SiO2 7.90, H2O 1.8, total 99.27. The empirical formula based on 83 O atoms pfu (i.e. Z = 1) is Pb24.12Mg8.74Mn1.25Fe0.94B1.03Al1.04C9.46Si9.39H14.27O83. The crystal structure was determined using single-crystal X-ray diffraction data. The new mineral is triclinic, space group P $$\bar{1}$$ , with a = 9.315(1), b = 9.316(1), c = 26.463(4) A, α = 83.295(3)°, β = 83.308(3)°, γ = 60.023(2)°, V = 1971.2(6) A3. The crystal structure of roymillerite is based built by alternating pyrophyllite-type TOT-modules Mg9(OH)8[(Si,Al)10O28] and I-blocks Pb24(OH)6O4(CO3)10(BO3,SiO4). The strongest lines of the powder X-ray diffraction pattern [d, A (I, %) (hkl)] are: 25.9 (100) (001), 13.1 (11) (002), 3.480 (12) (017, 107, −115, 1–15), 3.378 (14) (126, 216), 3.282 (16) (−2–15, −1–25), 3.185 (12) (−116, 1–16), 2.684 (16) (031, 301, 030, 300, 332, −109, 0–19, 1–18), 2.382 (11) (0.0.–11). Roymillerite is named to honor Dr. Roy McG. Miller for his important contributions to the knowledge of the geology of Namibia.

Yangite, PbMnSi3O8·H2O, a new mineral species with double wollastonite silicate chains, from the Kombat mine, Namibia

A new chain-silicate mineral species, yangite, ideally PbMnSi 3 O 8 ·H 2 O, has been found on a specimen from the Kombat mine, Otavi Valley, Namibia. Associated minerals are melanotekite and rhodochrosite. Yangite is colorless to pale brown in transmitted light, transparent with white streak and vitreous luster. Broken pieces of yangite crystals are bladed or platy, and elongated along [010]. It is sectile with a Mohs hardness of ~5; cleavage is perfect on {101} and no twinning or parting was observed. The measured and calculated densities are 4.14(3) and 4.16 g/cm 3 , respectively. Optically, yangite is biaxial (−), with n α = 1.690(1), n β = 1.699(1), n γ = 1.705(1), Y = b, Z ^ c = 11°, and 2 V meas = 77(2)°. It is insoluble in water, acetone, and hydrochloric acid. An electron microprobe analysis demonstrated that the sample was relatively pure, yielding the empirical formula (with calculated H 2 O) Pb 1 . 00 Mn 1 . 00 2 + Si 3 . 00 O 8 ⋅ H 2 O . Yangite is triclinic and exhibits space group symmetry P 1 ¯ with unit-cell parameters a = 9.6015(9), b = 7.2712(7), c = 7.9833(8) A, α = 105.910(4), β = 118.229(4), γ = 109.935(5)°, and V = 392.69(7) A 3 . Its crystal structure is based on a skeleton of double wollastonite SiO 4 tetrahedral chains oriented parallel to [010] and interlinked with ribbons of Mn- and Pb-polyhedra. Yangite represents the first chain silicate with two-connected double chains and possesses all of the structural features of a hypothetical triclinic Ca 2 Si 3 O 8 ·2H 2 O phase proposed by Merlino and Bonaccorsi (2008) as a derivative of the okenite structure. The difference in the H 2 O component between the hypothetical phase and yangite likely is a consequence of the larger Pb 2+ with its lone-pair electrons in yangite replacing the smaller Ca 2+ in the hypothetical phase.

Formation of secondary hematite and its role in attenuation of contaminants at mine tailings: review and comparison of sites in Zambia and Namibia

Mine tailings in African countries Zambia and Namibia have been investigated with an objective to determine the role of secondary hematite in immobilization of contaminants. Two sites, Chambishi and Mindolo, are located in the Copperbelt in Zambia with relatively humid climates and two sites, Berg Aukas and Kombat, are in Namibia, where the climate is semiarid. At the Chambishi site which is about 40 years old, a hardpan composed of hematite and gypsum has formed at a depth of about 60 cm and large amounts of Cu and Co have been deposited. At the much younger Mindolo site (30 years old, but most V remains in primary descloizite, embedded in a carbonate matrix while a relatively small amount of released V is incorporated into hematite. In contrast, released Zn and Pb are incorporated mainly into smithsonite and cerussite, which are less stable from an environmental viewpoint. Finally, at the Kombat mine tailings (< 5 years old), As released from pyrite is also incorporated into hematite, but Cu released by dissolution of chalcopyrite and bornite has precipitated as malachite, which is less stable than hematite. Water-leached concentrations of contaminants such as Cu, Zn, and Pb (also present in some carbonate phases) are an order of magnitude higher than water-leached concentrations of V and As which are bound to crystalline ferric minerals such as hematite and soluble only in the aqua regia fraction of sequential extraction. It seems that rapid formation of hematite under tropical climate conditions and incorporation of contaminants into this mineral phase is favourable for attenuation of released contaminants. These findings have implications at other mining sites with similar climates in Africa, South America and Asia.

Assessment of agricultural soil contamination by potentially toxic metals dispersed from improperly disposed tailings, Kombat mine, Namibia

The Kombat tailings dam, surrounded by agricultural lands, has been exposed to water and wind erosion over a long period of time. The objectives of this research were: (1) to characterize the tailings and the surrounding agricultural soils with respect to the mineral and trace element composition; (2) to determine the degree of soil pollution using soil contamination indicators; (3) to assess the environmental risk of polluted agricultural soil; and (4) to identify dominant type (mechanical and/or chemical) and dominant agent (water and/or wind) of metal dispersion from the tailings. A sequential extraction procedure was used to determine binding mechanisms involved in the retention of metals in tailings and soils under the influence of tailings, which indicate the trace metals bioavailability, the threat to groundwater pollution, as well as the dominant type of dispersion. Among seven analysed elements, copper and lead showed significantly high concentrations in tailings, especially in dry season (up to 9086mg/kg and 5589mg/kg, respectively). As a consequence, adjacent arable soils have high concentrations of Cu and Pb (up to 150mg/kg and 164mg/kg, respectively). Enrichment factors for lead and copper reveal severe contamination, while geoaccumulation indices disclose moderate to strong contamination by both elements. The combined pollution index points out high contamination. The main binding phase for Cu and Pb is the reducible fraction (oxides, hydroxides, oxyhydroxides). Similar metal distributions in the sequential extraction fractions of tailings and soils support the assumption that wind and water disperse tailings predominantly by mechanical transport to the surrounding agricultural soil. Although agricultural soils are contaminated with Pb and Cu, these metals are relatively strongly bound to the soils and are of medium risk for their mobilisation after The Risk Assessment Code (up to 20% for Cu and up to 36% for Pb). Though rehabilitation of tailings dam, as well as limitation of certain crop use on polluted agricultural land, is recommended.

Carlfrancisite: Mn32+(Mn2+,Mg,Fe3+,Al)42(As3+O3)2(As5+O4)4[(Si,As5+)O4]6[(As5+,Si)O4]2(OH)42, a new arseno-silicate mineral from the Kombat mine, Otavi Valley, Namibia

Carlfrancisite, Mn32+(Mn2+,Mg,Fe3+,Al)42(As3+O3)2(As5+O4)4[(Si,As5+)O4]6[(As5+,Si)O4]2(OH)42, is a new mineral from the Kombat mine, Otavi Valley, Namibia, and occurs as curved platy aggregates ~2 cm across on a matrix of Mn arsenates and oxides. It is yellowy orange to pale yellow with a very pale-yellow streak, translucent with a vitreous to opalescent luster, and does not fluoresce under ultraviolet light. Cleavage is micaceous on {001}, and no parting or twinning was observed. Mohs hardness is 3, and carlfrancisite is brittle with a hackly fracture. The calculated density is 3.620 g/ cm3. Optical properties were measured with a Bloss spindle stage for the wavelength 590 nm using a gel filter. The indices of refraction are e = 1.756, w = 1.758, and it is non-pleochroic. Carlfrancisite is trigonal, space group R3̄c, a = 8.2238(2), c = 205.113(6) Å, V = 12 013.5(4) Å3, Z = 6, c:a = 1:24.941. The seven strongest lines in the X-ray powder-diffraction pattern are as follows: d (Å), I, (hkl): 2.826, 100, (2̄ 2 44); 2.371, 88, (2̄ 3 40, 1̄ 3 41); 1.552, 84, (1̄ 5 0); 2.676, 63, (2̄ 3 7); 3.243, 54, (0 1 56, 1̄ 2 39); 4.107, 48, (1̄ 2 0); 2.918, 47, (0 2 40). Chemical analysis by electron microprobe and crystalstructure refinement gave As2O5 13.07, As2O3 3.18, P2O5 0.50, V2O5 0.74, SiO2 8.96, Al2O3 0.78, FeO 0.22, MnO 53.25, MgO 9.37, H2O(calc) 8.42, sum 98.49 wt%. The H2O content and the valence states of As were determined by crystal-structure analysis. The empirical formula is Mn2+ 33.55Mg10.39Fe2+0.14Al0.68 As3+1.44(Si6.67P0.32V5+ 0.37As5+5.08)O54 (OH)42 on the basis of 96 anions with (OH) = 42 apfu. The structure of carlfrancisite is closely related to that of mcgovernite and turtmannite.

Crystal chemistry of layered Pb oxychloride minerals with PbO-related structures: Part I. Crystal structure of hereroite, [Pb32O20(O, )](AsO4)2[(Si,As,V,Mo)O4]2Cl10

The crystal structure of hereroite, a new complex lead oxychloride mineral from the Kombat Mine, Grootfontein, Namibia, has been solved by direct methods and refined to R1 = 0.054 for 6931 unique observed reflections. The mineral is monoclinic C2/c, a = 23.139(4), b = 22.684(4), c = 12.389(2) Å, β = 102.090(3)°, and V = 6358.8(18) Å3. The structure contains 16 independent Pb sites in strongly asymmetric coordination by O and Cl atoms. There are two tetrahedral sites, from which one (As) is occupied solely by As, whereas the second (T) has the mixed occupancy of [Si0.48As0.29V0.15Mo0.09]. There are in total 21 O sites. The O1-O8 sites belong to the AsO4 and TO4 tetrahedral oxyanions. The other O atoms (O9-O20) are tetrahedrally coordinated by Pb atoms, thus being central for the OPb4 oxocentered tetrahedra. The OPb4 tetrahedra share edges to form the [O21Pb32]22+ layers that can be described as derivatives of the [OPb] layer from the structure of tetragonal PbO (litharge). The [O21Pb32]22+ layer in hereroite can be obtained from the [OPb] layer by removal of blocks of oxocentered tetrahedra, which results in formation of double-square sevenfold and square fourfold cavities. The cavities are occupied by the AsO4 and TO4 tetrahedra, respectively. The topology of the [O21Pb32]22+ layer is complex and can be described as a combination of modules extracted from the layers of OPb4 tetrahedra present in the structures of kombatite and symesite. The topological functions of tetrahedra within the layer are analyzed using the square lattice method, which shows that each symmetry-independent tetrahedron has its own topological function in the layer construction. The structure of hereroite belongs to the 2:1 type of layered Pb oxyhalides and consists of alternating PbO-type layers and Cl sheets oriented parallel to the (010) plane.

Crystal chemistry of layered Pb oxychloride minerals with PbO-related structures: Part II. Crystal structure of vladkrivovichevite, [Pb32O18][Pb4Mn2O]Cl14(BO3)8{middle dot}2H2O

The crystal structure of vladkrivovichevite, a new complex lead oxychloride mineral from the Kombat Mine, Grootfontein, Namibia, has been solved by direct methods and refined to R1 = 0.048 for 3801 unique observed reflections. The mineral is orthorhombic, Pmmn, a = 12.759(1), b = 27.169(4), c = 11.515(1) Å, and V = 3992.0(9) Å3. The structure of vladkrivovichevite belongs to a novel type of layered Pb oxychloride structure. The structure contains 12 symmetrically independent Pb sites. All Pb sites have strongly asymmetric coordination. Two B atoms form slightly distorted BO3 triangles. One symmetrically independent Mn atom forms five Mn-O bonds and one Mn-Cl bond by forming MnO5Cl octahedra. The O1, O2, O10, O11, and O12 atoms are tetrahedrally coordinated by four Pb atoms each, forming OPb4 oxocentered tetrahedra. The O7 site has a remarkable octahedral coordination, consisting of four Pb and two Mn atoms. The O1Pb4, O2Pb4, O10Pb4, and O11Pb4 tetrahedra share common edges to produce bands interconnected by O12Pb4 tetrahedra, forming a [O18Pb32]28+ layer. A O7Pb4Mn2 heterometallic oxocentered octahedron serves as the core of the [OPb4Mn2Cl2(BO3)8]16- clusters that link to the [O18Pb32]28+ layer via BO3 triangles. The presence of [OPb4Mn2Cl2(BO3)8]16- clusters is associated with large cross-like vacancies in the [O18Pb32]28+ layer.

Hereroite and vladkrivovichevite: two novel lead oxychlorides from the Kombat mine, Namibia

AbstractTwo new lead oxychloride minerals, hereroite [Pb32(O, ☐)21](AsO4)2((Si,As,V,Mo)O4)2Cl10 and vladkrivovichevite [Pb32O18][Pb4Mn2O]Cl14(BO3)8·2H2O occur in association with asisite, damaraite, kombatite, sahlinite, copper, quartz, barysilite, Mn silicates and a number of Mn oxyhydroxide minerals on a specimen from the Kombat mine in Namibia. The minerals formed as late-stage products of hydrothermal reworking of primary sulfide minerals.Hereroite is monoclinic, C2/c with a = 23.14(1), b = 22.65(1), c = 12.39(1) Å, β = 102.00(5)°, V = 6351.6(41) Å3 from powder-diffraction data and a = 23.139(4), b = 22.684(4), c = 12.389(2) Å, β = 102.090(3)°, V = 6358.8(18) Å3 from single-crystal data. It is bright orange, with white streak and adamantine lustre. It is brittle with no observed parting or cleavage and has a conchoidal fracture. The calculated density is 8.15 g cm–3. The mean refractive index in air at 589 nm is 2.38. The six strongest reflections in the X-ray powder diffraction pattern [d in Å, (I), (hkl)] are as follows: 2.982(100)(51); 2.795(47)(80); 1.986(24)(8); 1.641(24)(11..); 3.512(23)(61); 3.901(21)(511). Hereroite is named for the Herero people, one of the indigenous tribal groupings in the region where the Kombat mine is located.Vladkrivovichevite is orthorhombic, Pmmn with a = 12.87(5), b = 27.7(4), c = 11.46(3) Å, V = 4080.1(5) Å3, from powder-diffraction data and a = 12.759(1), b = 27.169(4), c = 11.515(1) Å, V = 3992.0(9) Å3, Z = 2, from single-crystal data. It is pale greenish yellow, with white streak and adamantine lustre. It is brittle with no observed parting or cleavage and has a conchoidal fracture. The calculated density is 7.40 g cm–3. The mean refractive indices in air at 589 nm are 2.30 and 2.34. The six strongest reflections in the X-ray powder diffraction pattern [d in Å, (I), (hkl)] are as follows: 2.860(100)(370); 2.733(84)(073); 3.707(49)(073); 3.068(37)(401); 2.075(32)(473); 1.601(32)(3.14.3). Vladkrivovichevite is named in honour of Prof. Dr Vladimir Gerasimovich Krivovichev (b. 24.04.1946), Head of the Department of Mineralogy, Geological Faculty, St Petersburg State University.The crystal structures of hereroite and vladkrivovichevite consist of alternating litharge-like O – Pb double layers and chlorine sheets and both are structurally related to other layered lead oxychlorides. In hereroite, tetrahedral AsO4 and (Si, As, V, Mo)O4 groups locate in defects within the O – Pb block, which combines square 'symesite-type' and double-square 'kombatite-type' cavities in its crystal structure. The structure of vladkrivovichevite is based on O – Pb derivative blocks with the interlayer occupied by Cl– anions and oxocentred OPb4Mn2 octahedra whose eight triangular faces are capped by triangular borate anions, BO33–.

Description and crystal structure of turtmannite, a new mineral with a 68 Å period related to mcgovernite

Jacobsite-rich Fe-Mn ores of probable Dogger age fill paleokarst pockets in the Triassic marbles of the Barrhorn Unit under Pipjigletscher in the Turtmanntal, Valais, Switzerland. These ores and embedding rocks underwent Tertiary metamorphism under upper greenschist facies conditions. Some of these jacobsite ores contain minor amounts of a yellow micaceous mineral, which appears to be a new Mn-Mg silicate-vanadate-arsenate that was named “turtmannite” with respect to the type locality. Turtmannite flakes up to 200 μm in length occur parallel to the main schistosity, or fill thin discordant veinlets. Turtmannite is rhombohedral R3̄c, with a H = 8.259(2) and c H = 204.3(3) Å in the hexagonal setting. The corresponding primitive rhombohedral cell has a R = 68.31 and α R = 6.92°. HRTEM images indicate that turtmannite is perfectly ordered along c. The structure of turtmannite has been solved to a final R1 of 12.4% on a Siemens Smart CCD diffractometer with MoKα X-radiation, and a detector to sample distance extended to 12 cm. The structure consists of 84 oxygen layers stacked along c, with twelve close-packed layers followed by two non-close-packed layers. This sequence is repeated six times. The structure contains eight symmetrically distinct cation layers. Three different occupational variants have been recognized leading to the following hypothetical end-member formulae and approximate abundances: I [IV] Mn 1.5 [IV] Mg 3 [VI] (Mn,Mg) 21 [(V,As)O 4 ] 3 [SiO 4 ] 3 O 5 (OH) 20 , 50% II [IV] Mn 1.5 [VI] (Mn,Mg) 21 [(V,As)O 4 ] 3 [SiO 4 ] 3 [AsO 3 ](OH) 21 33% III [IV] Mn 1.5 [VI] (Mn,Mg) 21 [(V,As)O 4 ] 3 [SiO 4 ] 2 [SiO 3 OH](OH) 25 16% The simplified chemical formula for turtmannite can be written as: (Mn,Mg) 22.5 Mg 3-3x [(V,As)O 4 ] 3 [SiO 4 ] 3 [AsO 3 ] x O 5-5x (OH) 20+x . The unit cell of turtmannite is similar to those of mcgovernite, a Mn-Mg-Zn arsenate from Sterling Hill, New Jersey, and an unnamed “mcgovernite-like” Mn-Mg arsenate from the Kombat Mine, Namibia. The crystal structure of turtmannite is close to the model predicted for mcgovernite by Moore and Araki (1978)

Removal of heavy metals from mine water by carbonate precipitation in the Grootfontein-Omatako canal, Namibia

Water from the Kombat mine was delivered to the Omatako dam via the 263-km-long Grootfontein-Omatako canal during test runs in 1997. It is intended to supply water from Kombat and other underground mines in the Otavi Mountain Land to the capital Windhoek. The Cu-Pb-Zn orebodies are hosted by carbonate rocks and the mine waters are supersaturated with respect to calcite and CO2. Along the length of the canal, the CO2 partial pressure drops from 10−2.1 atm at the inlet of the Kombat mine to 10−3.5 atm at the end of the canal. This is accompanied by a drop in Ca concentration from about 60 to about 20 mg/l. The heavy metal concentrations (Cd, Cu, Mn, Pb and Zn) drop along the course of the canal to values far below the national drinking-water standard. Scavenging by calcium carbonate precipitation is the major depletion mechanism.

Mechanism of the SiO4for CO3substitution in defernite, Ca6(CO3) (sub 1.58) (Si2O7) (sub 0.21) (OH)7[Cl (sub 0.50) (OH) (sub 0.08) (H2O) (sub 0.42) ]; a single-crystal X-ray study at 100 K

Defernite, Ca6(C03)L5s(Si207)o.21(OHMClo.5o(OH)o.os(H20)od, is a carbonate mineral [space group Pnam; at 100 K: a = 17.744(2), b = 22.601(4), c = 3.633(1) A, Z = 4] with zeolitelike structural channels. The structural framework is formed by edge- and comer-sharing Ca06_7 polyhedra, which are additionally linked by C03 groups aligned parallel to the (001) plane. This framework has channels parallel to the c axis, confined by eight-membered rings of Ca06_7 polyhedra. The inner surface of the channels exposes H atoms of OH groups bonded to Ca. The framework carries a positive charge, which is balanced by small anions (mainly Cl) in the structural channels. The crystal structure of defernite from the Kombat mine, Namibia, was refined using 3845 reflections to R = 2.6% at 100 K. The low but ubiquitous Si02 concentrations (1-5 wt%) observed in chemical analyses of this mineral were structurally located. Defernite has two symmetrically distinct C03 groups (Cl, C2), which are repeated by a mirror plane parallel to (001). The C2 double layer of C03 groups is partially replaced by a disilicate Si207 unit, where an additional 0 atom is accommodated between the two 0 triangles of the former C03 groups. This substitution is observed only for C2. In addition, all H atoms on the surface of the structural channels were located and refined. Cl in the center of the channel is bonded to six H within 2.8 A. Defernite may form a solid solution between Ca6 (C03)2 (OH)7 [Cl,OH] and Ca6(C03)l.o(Si207)oAOH)7, in which the latter end-member is characterized by a neutral framework and structural channels without charged ions.

Damaraite, a new lead oxychloride mineral from the Kombat mine, Namibia (South West Africa)

AbstractDamaraite, ideally 3PbO.PbCl2, is a new mineral which occurs with jacobsite, hausmannite, hematophanite, native copper, an unnamed Pb-Mo oxychloride, calcite, and baryte, in specimens from the Asis West section of the Kombat mine, Namibia (South West Africa). Damaraite is colourless and transparent with a white streak, and adamantine lustre. It is brittle with an irregular to subconchoidal fracture and a cleavage on (010). The mineral has a low reflectance, a weak bireflectance, barely discernible reflectance pleochroism, from grey to slightly bluish grey in some sections, and is weakly anisotropic. Reflectance data in air and in oil are tabulated. Colour values relative to the CIE illuminant C for the most strongly bireflectant grain are, for R1 and R2 respectively:It has a VHN50 of 148 (range 145–154) with a calculated Mohs hardness of 3. X-ray powder diffraction studies give the following parameters refined from the powder data: orthorhombic; space group Pma2, Pmam or P21am; a 15.104(1), b 6.891(1), c 5.806 (1)Å; V is 604.3 (4)Å3 and Z = 3. Dcalc 7.84 g/cm3. The strongest six lines of the powder pattern are [d in Å (I) (hkl)]: 2.902 (10) (121,002); 2.766 (10) (510,221); 2.877 (9) (411); 3.164 (6) (401); 3.135 (6) (220); 1.747 (b) (313,721,531). The name is for the Damara sequence which hosts the Kombat deposit.

A sakhaite-like mineral from the Kombat Mine in Namibia

AbstractSakhaite from the Kombat Mine in Namibia is cubic, with a = 14.749(1)Å; the space group is a subgroup of Fd3m, the density is 2.88 g/cm3, and the index of refraction is n = 1.642(2). It is apparently more highly hydrated than previously described sakhaite, and has more aluminosilicate substitution. The idealized composition is Ca24Mg8(BO3)8[(BO3)y{AlSi4(O,OH)&lt;16}x](CO3)8.&lt; 8H2O with x = 0.73 and y = 5.0.

Johninnesite, a arsenosilicate from new sodium manganese the Kombat Mine, Namibia

AbstractJohninnesite, ideally Na2Mg4Mn12As5+2 Si12043(OH)6,, is triclinic, P1 or P1̄, with a = 10.44(2), b = 11.064(6), c = 9.62(1) Å, α = 107.43(7), β = 82.7(1), γ = 111.6(1)°, V = 894(2) Å3, and Z = 1. It occurs as yellow-brown fibrous aggregates, associated with rhodonite, kentrolite, and richterite, from the Kombat Mine in Namibia. Johninnesite has cleavages on {100} and {010}, density of 3.48 (meas.), 3.51 (calc.) g/cm3. It is biaxial negative, with 2Vx = 41.9°, α = 1.6742(4), β = 1.6968(3), γ = 1.6999(3); dispersion r &gt; υ, distinct.