American Mineralogist, Volume 64, pages 6E6-889, 1979

Cuprohydromagnesiteand cuproartinite, two newminerals from Gabbs,Nevada

SrnNlnvG. Oswnln,'.NoWrr-soN W. Cnoor. III Mobil Oil Corporation,P.O. Box 5444 Denuer,Colorado 80217

Abstract

Cuprohydromagnesiteand cuproartinitewere found with other secondarycopper minerals in the brucite zoneof the BasicRefractories Mine at Gabbs,Nye County,Nevada. Cuprohydromagnesite,(Cu,Mg)5(CO'L(OH)b.4HrO, occurs as a supergenealteration productof primary coppersulfides and magnesite-brucite-serpentinerock. Associatedminer- als iirclude chalcopyrite,bornite, magnesite,antigorite, chlorite, brucite, hydromagnesite, artinite,huntite, alumohydrocalcite,callaghanite, mcguinnessite,r and nakauriite.The trans- lucentblue crystals are bladed, elongated along the c axisand flattened on {010}.Cuprohydro- magnesiteismonoclinic,spacegroupP2r/c,a: 10.653(3),0= 9.141(l),c= 8.570(2)A,A: ll5o23', Z : 2. The strongestlines in the X-ray powder pattern are 6.54(25)(110), 5.91(l00x0ll), 3.393(40)(121),2.954(60)(022),2,s73(25)(230),2.408(30X400), 2.247(40)(023),and 2.050(30X314).Cuprohydromagnesite is biaxial (+),2V = 36-38o;a : 1.562(2\,P:r.567(2),t=l.61aQ).G(meas)=2.548(5),G(calc):2.543.Thenameisforthe compositionand the relationto hydromagnesite. Cuproartinite,(Cu,Mg)r(CosXOH)r.3H2O, occurs as a supergenealteration phase directly associatedwith cuprohydromagnesite.Crystals are acicular,blue translucent,elongated on {010}as radiating fiber aggregates.It is monoclinic,space group C2, a : 16.E99(2),b = 3.272(l),c = 6.362(2)A,9: 100o40',Z = 2. The strongestlines in the X-ray powderpattern are E.30(4)(200),5.51(EX20l), 3.800(s)(401), 2.813(10Xlll), 2.283(3X5ll),and 1.919(3) (7ll). Cuproartiniteisbiaxial(-),2V = 70-73",a = l.5M(2'),P:1.596(2),t = 1.627(2). G(meas)is 2.186(5),G(calc) is 2.188. The nameis for the compositionand the relationto artinite.

Introduction als were the copper-dominantanalogues to hydro- In 1970one of the authors(SGO) found a richly magnesiteand artinite. mineralizedsupergene zone near the contact of pri- The names,cuprohydromagnesite and cuproarti- mary copper sulfidesand magnesite-brucite-serpen-nite, are for the compositionsand their relationships tine rock in one of the abandonedbrucite pits at the to hydromagnesiteand artinite. Both speciesand Basic RefractoriesMine near Gabbs, Nye County, their nameshave been approved by the Commission Nevada.Primary mineralsinclude chalcopyrite, bor- on New Minerals and Mineral Names,IMA. Type nite, antigorite,magnesite, brucite, and chlorite.As- materialhas been deposited in the SmithsonianInsti- sociatedminerals in the supergenezone are hydro- tution (NMNH #144188)and in the collectionsof the magnesite, artinite, huntite, alumohydrocalcite, CarnegieMuseum of Natural History. callaghanite,mcguinnessite, and nakauriite. In the supergenezone several small crystals of a bluebladed Occurrence mineraland a light blue acicularmineral were found Cuprohydromagnesiteoccurs as 0.5-5mm crystals intimately associatedwith hydromagnesiteand arti- aspart ofa supergenealteration zone. Cuproartinite, nite. Further investigationindicated that theseminer- found as small(0. l-2mm) acicularcrystals, occurs in direct associationwith cuprohydromagnesite,usually I Mcguinnessite,(Mg,Cu)rCOr(OH)6, is a new mineral recently with hydromagnesiteand artinite. The mines at approvedby the IMA Commrssionon New Mineralsand Mineral Gabbs havebeen actively mined since1937, first for Names. brucite and later for magnesite(Cleveland, 1963). ffi3-'on/')r' /7 9/0708-0886$02.00 886 OSWALD AND CROOK: CUPROHYDROMAGNESITE AND CUPROARTINITE EE7

The magnesiumdeposits are located in the upper dolomite memberof the TriassicLuning Formation, and wereformed by the dissolutionof dolomitebeds by hydrothermalsolutions which migrated upward and recrystallizedas massivereplacement bodies of magnesite.The magnesiteunits were then subjected to complex folding, faulting, low-grade regional metamorphism,dolomitization, and intrusion by dikes, sills, and a granodioritestock. The igneous intrusion formed two small bodies of brucite and minor tactite zonesaround the dikes and sills. Ter- tiary block faulting, uplift, and erosionexposed the ore bodies. Fig. l. Morphologicaldevelopment of cuprohydromagnesite. = : = Cuprohydromagnesite Formsare a {010},c {001},r {310}. Physicalproperties is P2t/c. Systematicextinctions were observedfor Cuprohydromagnesiteoccurs as bladed crystals, {0&0}with k : 2n * I and for Ih0ll with/ : 2n * L elongatedalong the c axis and flattenedon {010}as The powder data (Table l) are comparableto those sprays,crusts, and powderycoatings. Principal forms of hydromagnesite(Jcros Card No. 25-513). include{001}, {010}, and {310}(Fig. l). Indiceswere Twinning, which is almost constant in hydro- obtainedby goniometricmeasurements. The crystals magnesite,is presentin cuprohydromagnesitebut to are brittle with a perfect{010} cleavage. Crystals have a lesserextent. A prominent pseudo-orthorhombic a vitreous to silky luster, are translucent,and pale cell of space group 8222 is present in hydro- blue to blue in color. The color intensity increases magnesiteand has beenused by previousresearchers with increasingcopper content. Mohs hardnessis (Murdoch, 1954;Bariand et al., 1973)to indexthe approximately3Vz. The streakis white. powder data. A pseudo-orthorhombiccell is present Cuprohydromagnesiteis biaxial (*) 'efractivein- in cuprohydromagnesitebut, like the twinning, it is dices(NaD)a = 1.562(2),P= 1.567(2),7= poorly developed. 1.614(2),2V= 36-38".It is weaklypleochroic with a = colorlessto paleblue, B = paleblue,7 : paleblue Chemicalanalysis to light blue.Optical orientation is b : Z, c:X : 48". An electron microprobe analysis(Table 2) was Specificgravity was determinedin toluene on a used in the identificationof cuprohydromagnesite, Bermanbalance by averagedrepeated measurements due in part to the lack of sufficientmaterial for a on l6mg of material;G(meas) is 2.548(5),G(calc) is standard chemicalanalysis. The analysiswas con- 2.543. The specificgravity was calculatedusing a ducted with 150 nA specimencurrent and 12 kV value of Z = 2, basedon the mineral'sisostructural excitation voltage. Microprobe standardsused for relationship with hydromagnesite. Cuprohydro- the followingelements are: Cu, Fe (analyzedCu-Fe- magnesitegives off a light blue fluorescenceunder Ni alloy); Mg (magnesite);Ca (calcite).COz was short-waveultraviolet radiation. measuredby gravimetricanalysis using absorption tubesand acid decomposition.Water was measured X-ray crystallography by total weight loss on ignition minus the COz con- Unit-cell parametersfrom Weissenbergand pre- tent.The presenceof COz,HrO(* ), and HrO(- ) was cession photographs using CuKa radiation confirmedby DTA, TGA, and DTG analysis.Cor- (1.54051A)(estimated standard deviations in paren- rectionswere made using the Euplon VII programof theses)are a = 10.653(3),b = 9.141(l),c = 8.570(2), Rucklidgeand Gasparrini(1969). Tests for Mn, Ti, 9 : ll5'23', Z : 2, V : 753.97A8.Lattice parame- Zn, Na, K, F, and Cl werenegative. The mineral is ters were obtainedfrom a least-squaresrefinement. readilysoluble in most mineral acids. The cell parametersare comparableto those of hy- Normalization of the analysis(Table 2, analysis dromagnesite,which is monoclinic,P2t/c, a = l0.ll, l) yields the empirical formula (Cuo.r'rMg'.or.Fq.og b : 8.94,c= 8.384,0 : 114"35',Z : 2(Bariandet Cao.ooz)(COs)r.r'o(OH)r.rro.3.884HrO, based on 5 to- al., 1973).The spacegroup of cuprohydromagnesite tal cations. This yields the ideal formula unit of 888 ost4lALD aND cRooK: CUzR1HvDRqMAGNESITEAND CUzR,ARTINITE

Table l. X-ray powderdata for cuprohydromagnesite mineral. In the structure,the magnesiumsites are composedof 4(MgCOr) + Mg(OH)6 in the asym- d d- hkr obs carc metricunit. Both magnesiumatoms are octahedrally coordinated,to form a three-dimensionalframework 9.63 9.625 100 20 of MgO. octahedraand triangular carbonateions 5.53 6.628 llA 25 5. 9l 5. 908 011 t00 (Akao et al.,1974). Judgingfrom the differencebe- 4.8I0 4.8L2 200 4.570 4.570 010 IO tweenMg-O (or OH) distancesin thesesites, prefer- entialsubstitution of Cu for Mg into the MgCO, sites 4.28L 4.283 loz 4.259 4.258 2I0 l0 is highly probable.Thus the taxonomicalboundary 4. 130 4.L29 LZU drawn hydromagnesite 3. 870 3.871 002 10 between and cuprohydro- 3.565 3.555 0L2 15 magnesiteat Cu:Mg = l: I appearsto be meaning- 3.393 3.393 121 40 less.The preferentialsubstitution of copperfor mag- 3. 312 3.3r4 220 l0 nesium is verified by the electron microprobe 3.2s0 3.247 211 3. 151 3.154 102 analyses,none of which show a coppersubstitution 2.980 2.982 LL2 10 of greaterthan 4 of the 5 total cation sites. 2.934 2.954 o22 50 2.90r 2.905 130 t 2.832 2.835 031 l Cuproartinite 2.767 2.766 22L 20 2.690 2.689 113 Physicalproperties 2. 510 2. 611 131 5 2.600 2.596 L22 ) Cuproartiniteoccurs as crustsof acicularcrystals, 2.573 2.374 230 25 elongatedon and as sphericalaggregates of 2.533 2. 533 202 {010}, 2.482 2.484 013 radiatingfibers. Principal forms include{001}, {100}, 2.408 2.406 400 30 {010},and {201}.The crystalsare brittlewith a perfect 2.287 2.285 040 f cleavage.Crystals have a vitreous to silky 2.247 2.247 vz5 40 {100} 2.222 2.223 140 IO luster, are translucent,and pale blue to blue (the 2.2L3 2.2L5 222 f color intensityvaries with the coppercontent). Mohs 2. L95 2.196 113 20 hardnessis approximately2Yz. The streakis white. 2.190 2. LgL 132 l0 2.1tll 2. L42 204 f Cuproartinite is biaxial (-), refractive indices 2.085 2.085 2L4 l0 (NaD) a : 1.544(2), = 1.596(2), : 1.627(2),2V 2. 050 2.049 314 30 0 t = 70-73".It is weaklypleochroic with axialcolors a 2.029 2.027 123 15 = : = 2. 018 2. 015 142 5 colorless,B colorlessto paleblue, 7 paleblue. Optical orientationis b : Y, c:Z = 131". U4.6 tm Debye-Scherrer camera using CuKa radiation. Specificgravity was determinedin toluene on a Ineensities visually estimated, Bermanbalance by averagedrepeated measurements

(Cu,Mg),(COs).(OH)r.4HrOwhere Cu)Mg. The Table 2. Chemicalanalysis of cuprohydromagnesite material is thus the copper-dominantanalogue of hydromagnesite. 1 2 Copper substitution varies from CUO 45.43 40.62 __:__ 3.02 to 3.70 of the 5 total cation sites in analyzed FeO 0.27 0.28 materials.Although the mineral hasa variablecom- position,in all studiedspecimens (6) the coppercon- Mgo 10.90 13.44 43.10 tent is well over 50 mole percentof the total cation cao 0.06 0.r9 site. An electron microprobe study of 20 hydro- co2 29.0L 30.10 37.64 magnesitecrystals from the samearea shows * some L>. LZ 15.79 L9.26 Cu substitutionfor Mg, but neverover l0 atom per- "rot centof the total 5 cations.Thus theredoes not appear TOTAI, 100.79 100.4 2 100. 00 to be a complete seriesfrom hydromagnesiteto 1,2) Gabbs, Nye county, Nevada. cuprohydromagnesite.The name of cuprohydro- magnesiteis for materialwith Cu)Mg. 3) Theoretical hydromagnesite. * Measured by gravimetric analysis using Discussion absorption tubes andl acid dleconposition. ** The crystal structure HrO neasured by total weight loes on of hydromagnesitehas been ilnition nj.nus analyzed CO2 content. solvedbased on the pseudo-orthorhombiccell of the OSWALD AND CROOK: CUPROHYDROMAGNESITEAND CUPROARTINITE on crystals weighing l2mg; G(meas) is 2.186(5), Table 4 Chemical analysisof cuproartinite G(calc) is 2.188.The specificgravity was calculated using a value of Z : 2, based on the isostructural CUO 40.99 34.35 relationship with artinite. Cuproartinite gives off a pale blue fluorescenceunder short-wave ultraviolet Mgo 1r. 54 Is.96 4I.00 radiation. CaO 0.43 0.I7

X-ray crystallography co2' r7. 16 18.44 22.37 Unit-cell parametersfrom a Weissenberg pre- 29.46 30.40 36.63 and "2o** cessionstudy using CuKa radiation(1.54051A) (esti- TOTAL 99.58 99.32 100.00 mated standard deviations in parentheses)are a : = = : 16.899(2),b 3.272(t),c 6.362(2)A,P 100o40', I,2) Gabbs, Nye County, Nevada. Z = 2, V : 345.7A3.Lattice parameterswere ob- 3) Theoretical artinite, M92co3(oH)2.3H2o. tained from a least-squaresrefinement. The cell pa- * rametersare comparableto thoseof artinite, which is Measured by gravimetric analysis using absorption tubes and acid decomposition. monoclinic,space group C2,q: 16.56,b: 3.15,c: ** 6.22A,0 :99"9', Z:2. The spacegroup of cupro- measured. by total weight loss on "2oignition minus artinite is C2. The only extinctions observed were analyzed CO2 content. those correspondingto the C-centeredlattice, h + k : 2n. The powder data (Table 3) are comparableto Chemicalanalysis those of artinite (Jcens Card No. 6-484). An electronmicroprobe analysis (Table 4) was usedin the identificationof cuproartinite,due in part to the lack of sufficientmaterial for a conventional Table powder 3.X-ray datafor cuproartinite chemicalanalysis. The analysiswas conducted as de- scribedfor cuprohydromagnesite.Tests for Mn, Ti, dobs hk1 carc Zn, Fe, Na, K, F, andCl werenegative. The mineral is readilysoluble in mostmineral acids. U. JU 8.30 200 40 6 .25 6.25 00r 20 Basedon two total cations,the analyzedmaterial tr. f,l 5. s09 201 80 (Table 4, analysisI ) yieldsthe empiricalformula 4.60 4.602 20]- 10 of (Cut.rurMgorooCao.oosXCOa)o.r6s(OH 2.949H2O. !. L)Z 400 10 )2.o"n. This yields an ideal formula of (Cu,Mg), 3.800 ? ?oa a-or 50 (CO.XOH),.3H,Owhere Cu)Mg. The materialis 3.122 3.I22 202 Itr 2.900 2. 898 111 20 thus the copper-dominantanalogue to artinite.Cop- 2. 813 2..JL5 111 100 per substitutionin all studiedmaterial (5 specimens) 2. t55 2.754 402 10 is variable,ranging from 52 to 63 atompercent of the 2.300 2.30r !02 f, cationsite. Electron microprobe analysis of ten arti- 2.291 2.294 602 tr nitesfrom area partial a.z6J 2.283 5J-I 30 the showonly a substitutionof 2. I95 2.r98 312 10 Cu for Mg (maximumof l0 atom percent).Thus, as 2.101 2.097 5II 5 with cuprohydromagnesite,a complete solid solution 2.082 2.084 003 10 seriesdoes not appearto be present. 1.940 1.938 203 10 r. 919 l, . 918 711 30 References I QOO l. 900 802 5 (1974) I.762 Akao, M., F. Marumo and S. Iwai The crystal structureof r L.762 r 5I2 r5 L1.763 .711 (5 h ydrom agnesite. A ct a C rysr allog r., 83 0, 26'70-267 2. Bariand, P., F. Cesbron, H. Vachey and M. Sadradeh (1973)

I.720 L.720 113 f, Hydrom agnesitefrom Soghan, Ir an M ineral. R ecortl, 4, 18-20. 1. 681 r. 684 I0, ot tr (1963) 'I (On Cfevefand, J. H. Paragenesisof the Magnesite Deposit at t. s90 f, 204 Gabbs,Nye Counry, Neoada. Ph.D. Thesis, Department of Geol- 1.58I 1.583 02r f, ogy, Indiana University. 1. 570 1.568 22r 5 M urdoch,J. ( 1954)Unit cellof hydromagnesite.Am. Mineral.,39, l. 541 r.542 22L 5 24-29 I. 500 I.502 42t 5 Rucklidge,J. C. and E. L. Gasparrini(1969) Specifications of a Comptete Program for Processing Electron Microprobe Data: II4.5 mm diameter Debye-Scherrer camera using EM PA DR VIL Department of Geology, University of Toronto. CuKo radiation. Intensities visually estimated. Manuscript receiued, August 23, 1978; accepted Jbr publication, Nouember 28, 1978.