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Bartonite, a New Potassium Iron Sulfide Mineral

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Bartonite, a New Potassium Iron Sulfide Mineral American Mineralogist, Volume 66, pages 369-375, I98I Bartonite, a new potassium iron sulfide mineral GENaTO K. CZAMANSKE. RICHARD C. ENN U.S. GeologicalSurvey 345 MiddlSeld Road Menlo Park, Califurnia 94025 B. F. LEONARO U.S. GeologicalSumey Federal Center Denver,Colorado 80225 AND JOAN R. CTENX U.S. GeologicalSumey 345MiddkrteH Road Menlo Park, Califurnia 94025 Abstract The new mineral bartonite has been found in a mafic, alkalic diatreme at Coyote Peak, Humboldt County, California. Associated v/ith it are the two previously known potassium iron sulfideminsmls, djerfisherite,IQ(Fe,Cu,Ni)24S26C1, and rasvumite,KFerS3, as well as er- dite, NaFe2S3' 2IJ2O,and one or two other new sodium iron sulfide minerals. Bartonite has been found in discrete segregations of sulfide in which pyrrhotite pre- dominates. It is blackish brown, distinctly darker than pyrrhotite on fresh surfaces;in pol- ished section it is yellow, softer and darker than pyrrhotite, and anisotropic. Bartonite is tet- ragonaf l4/mmm, a : 10.424(l),c : 20.626(l)L, Z : 2; density for K5 7eFe21.2aS2ue33.366 g cm-3 (calc.),3.305(10) (meas.). The six strongestlines of the X-ray di.ffractionpowder pattern are (in A;: z.rqtoo;(224),5.99(77Xll2), 1.833(40)(408),9.31(27xl0l)' 3.r39Q7)(3r2)'and 2.379(25)(316).Reflectance in air at 540 nm [s209Vofor Ro, 2l.8Vofor R".. Microindentation hardness(VHN) at l5-gram load is 94-120,mean l(X+9. Introduction tion in November 1977.'Type specimenswill be de- posited at the National Museum of Natural History, Bartonite, djerfisherite, and rasvumite were noted Smithsonian Institution. in several representative polished sections of Coyote The geology and mineralogy of the diatreme at Peak material; they defied analysis and identification Coyote Peak have been briefly described by Cza- before we hypothesized that these yellowish green- manskeet al. (1977, 1980). grey sulfide phases might contain potassium. The petrologist name honors Paul B. Barton, Jr., sulfide Occurrence and Paragenesis with the United States Geological Survey, for his Bartonite is typically found associatedwith pyr- outstandingcontributions toward rigorous ulilization rhotite in rare sulflde-rich clots several centimeters of sutfrde mineral chemistry in the deciphering of ore side. Bartonite may oonstituteonly 10-15 per- genesis. Bartonite is the first sulfide mineral for on a which a radiometric ageQ9.4t0.5 m.y.) has been di- I was approved as a new mineral on the rectly determined(Czamanske et a1.,1978).The new Note that bartonite basisof the formula K3Fe1eS1a,and was ascribedthat formula by mineral and the name bartonite were approved by Czamanskeet at., 1978and 1979.More cautiously, it was called "a the Commission on New Minerals and Mineral new K, Fe-sulfide closely related to djerfisherite" by Czamanskeet Names of the International Mineralogical Associa- al.,1980. 0003-004x/8r/0304-0369$02.00 369 CZAMANSKE ET AL; BARTONITE cent of such masses,but areasseveral mm in dimen- sion may consist of equal portions of bartonite and pyrrhotite. A small amount of pyrite may also be present.Bartonite may be intimately intergrown with the typical silicates--phlogopite,schorlomite, acmite, clinopyroxene, nepheline, natrolite, and sodalite- that comprisethe host rock to the sulfide-rich clots. In many specimens,textures strongly suggestthat bartonite has replacedpyrrhotite (Figs. I through 3). However, it is unclear to what extent bartonite may also have replaced silicate matrix or, indeed, have been replaceditself by late crystallizing silicates.In places, bartonite is finely veined by one or more gangueminerals (Figs. I atd2), and someaggregates Fig. 2. Bright pyrrhotite, interpreted as a residual cuspate of bartonite contain inclusions of phlogopite and island being replacedby bartonite. 77-CYP-31,1.06 x 1.50mm. other gangueminerals. Figures I and,2 show typical bartonite-pyrrhotite replacing pyrrhotite along fractures. It also occurs relations. Bartonite embays pyrrhotite, and minute sparingly as veinlets in bartonite, as enclosuresin veinlets or cusps of the host pyrrhotite project be- gangue minerals that vein bartonite, as fringes of tween individual bartonite grains. Rarely, bartonite minute prisms on bartonite, and as small patchesbe- occursas small skeletalcrystals, as subhedralcores of tween bartonite and pynhotite. Bartonite has par- magnetite octahedra,and as atolls in equant in- tially altered to goethiteon one specimen. clusionsof ganguein pyrrhotite. Aggregatesof acicular,high-iron sphalerite(blades Observationto date has not revealedthe sequen- to 0.5 x 0.02 mm) are present in bartonite in one tial relations of bartonite to the other K and Na sul- sample;analyses show (wt.7o) Fe:24t1, Mn = 1.3, fides--djerfisherite, rasvumite, erdite (NaFeS, . 2H2O), Cd : 1.0.Also presentis a subhedralskeletal crystal .2HrO-as and NaFerS, it has not been seen with of loellingite(0.09 x 0.17mm) senfaining 1.6 wt.Vo them. Ni. Pyrrhotite, typically the dominant sulfide in barto- Small octahedra and platelets of magnetite are nite-bearing assemblages,occurs as irregular masses studdedthroughout someaggregates of bartonite and and occasionallyas tabular crystals.This pyrrhotite appearin someinstances to be localizedat bartonite- contains 47.3 atomic percent Fe (wt.Zo;Fe : pyrrhotite contacts(Fig. 3). Trains of magnetiteocta- : 61.2+0.3,S 39.1+0.3),and X-ray studyshows that hedra are much lessfrequently seenin pyrrhotite. Ti- it is a 5C ordered hexagonalpyrrhotite (Carpenter taniferous magnetite is an irnportant constituent in and Desborough,1964). the host rock, but the fine-grainedmagnetite associ- Pyrite commonly occursas fine-grainedaggregates Fig. 3. Concentration of sharply bounded, fine-grained Fig. l. Aa irregular remnant of bright pyrrhotite in a matrix of magnetite along itrterface between pyrrhotite (bright) and bartonite veined by silicates.Z7-Cyp-15. 1.3?x 1.94mm. bartonite, 77-CYP-31,0.72x 1.00mrn. CZAMANSKE ET AL.: BARTONITE t7l ated with bartonite and erdite (Czamanske et al., Table 2. Electron microprobe aoalyses of Cl-rich bartonite, phases intermediate to 1979) is nearly free of Ti and is interpreted to be a djerfisherite, rasvumite, and apparently bartonite and djerfisherite. later reactionproduct, perhapspartially in accommo- dation of iron releasedby replacement of pyrrhotite C1-rich barLonile (atomic FelS : 0.899)by bartonite (FelS : 0.762- 0.785). K r0.5(.2)** 10.6 10.5 10.3 10.4 10.5 Na -l** o.22(.02) o.20 0.20 ComPosition 116.8 Fe 50.3( ,4) 48.7 48,7 \8,2 49.0 Fe-sulfide Ni- 0.25(.03) o.116 0. 43 0.\2 0,011 0, 16 Analysesof bartonite and associatedK, Cu 0.52(.03) 0.66 0.77 0.81 0.93 3.36 phaseswere made on the ARL EMx-sMelectron mi- s 37.3(.6) 38.1 38.2 37.9 38.0 38.0 cL r.35(.05) r.38 r.3o \.23 0,78 0.82 croprobe at Menlo Park, California. (Analytical de- t roo.22 99.90 99.90 99.08 99.35 99.84 tails are noted in the footnote to Table l). Aside from the somewhat more massiveoccurrence and replace- Internediate PhaEes ment relation to pyrrhotite, the strongestindication 12qA q 134 that we were dealing with a phasedistinct from djer- fisherite was in the lower metal-tosulfur ratio char- K r.0.6 r0.5 10.r 9.10 9.15 9.20 9.30 Na 0.64 0.52 o.3q 0,06 - 0.78 0,58 study has shown q4.4 q9.8 acteristic of bartonite. Subsequent Fe \7 .2 \6.7 4?. 1 46.3 A5.7 that this distinction may be uncertain becausebarto- Ni. 0.60 1.30 1.51 0,95 2.37 r.36 0.08 LU 4.q{ 5.12 3.80 7.72 7 ,86 5, 16 2.98 nite compositionappears to vary. 3{. q 35.0 35.4 35.6 35.7 36.3 36.3 0.80 0.79 0.00 0. 00 1. 20 1.02 The compositionof chlorine-poorbartonite is rep- c1 0.95 resented by the five analyses (from two specimens) t 98.83 99.9U 99.04 99.73 99,q8 99.70 r0o.06 averagedin Table l; included is an analysis made on -Eessr.!g. the crystal fragment from which ths 5ingle-crystal 125A r3x 13? 133 data were collected for the structural analysis (Evans K 9.30 9,2O 9.oo 9.10 9.\5 15.8 Na o.o? 0.76 0.?6 0.04 0.r0 0.02 q5.0 q). Fe \7 .9 trS.q 45.4 \\.2 o Table l. Electron microprobe analysesof Cl-poor bartonite from Ni r. 64 r, 31 1,41 0.87 0.76 0.01 Coyote Peak, Humboldt County, California (weight percent). LU \.92 6.9r. 8.37 9.2r 9.69 0.00 3q.4 34.8 33.8 34.5 33.8 38.6 CI 0.80 1.20 r.26 1.10 r, rJ 0.01 Calculated t 99,58 r00.00 99,90 99.13 r00.04 Bartonite (5)* K5.6gFe29.z7sz6.93rr 99.03 rsample numbers preseneed bo allow insiSht inLo phase K 9.54 (9.44-9.7r) 10.01 association. Na 0.05 (0.02- 0.14) (50.8- 51.8) 51.05 **Indicates esti@ted uncertainty. For each anaLysis 6-8 poi'nts Ni 0.19 (0.r0- 0.31) were occupied for each distinct mineral phase. Co 0.lI (0.07- 0.17) rrr - indicates not sought. Cu 0.62 (0.56- 0.66) s 38.4 (37.6-39.r) 38.94 c1 q.02 (0.0r- 0,02) ----:_ ]00.r3 100.00 D calc. and Clark, l98l). Refinement of site populations in (e/cn31 for Z=2 3.333 3.286 the crystal structure analysis of the selected crystal fragment gives the formula Kr.urFero.rrSro(S)o'r,in good agreementwith the microprobe analysis of that *lndicates number of discrete areas analyzed (6-8 crystal, (K,Na)r ro(Fe,Ni,Co,Cu)rl.roS* r, (included in poinbs counLed) in specj,mens 15 and 31.
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