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Vein Minerals from the Tamworth and Parry Groups(Devonian and Lower Carboniferous), N.S.W

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Vein Minerals from the Tamworth and Parry Groups(Devonian and Lower Carboniferous), N.S.W THE AMERICAN MINERALOGIST, VOL. 46, SEPTEMBER.OCTOBER, 196I VEIN MINERALS FROM THE TAMWORTH AND PARRY GROUPS(DEVONIAN AND LOWER CARBONIFEROUS), N.S.W. Knrrn A. W. Cnoox, (Jniaersityof New England.,Armid.ole, N.S.W.,Australia.* ABsrR-A.cr Veins in the Tamworth and Parry Groups bear the following minerals: calcite, laumon- tite, stilbite, heulandite, prehnite, pumpellyite, epidote, axinite, chlorite, muscovite, quartz, albite, bytownite, and amphibole. The stratigraphic distribution of each species is difierent. Mineral assemblages are characteristic of the albite-epidote mineral facies, the prehnite-pumpellyite facies, and the laumontite subfacies and heulandite-analcite subfacies of the zeolite facies. Those characteristic of the first two facies occur in irregular veins, those of the heulandite-analcite subfacies in joints, and those of the laumontite subfacies in bedding veins, faults and shear zones. Comparison with the stratigraphic distribution of diagenetic minerals indicates the ir- regular veins are diagenetic. Later the zeolite facies veins formed under lower P-T condi- tions, those in the joints being earliest and characteristic of the lowest P-T conditions. A quartz-bytownite-amphibolb vein in a hornfels, thought to be a metamorphosed laumontite-chiorite vein, is described. INrnooucrroN The Tamworth and Parry Groups, which are the lowest units in the Tamworth Trough sequenceof western New England, New South Wales (Fig. 1) have been describedstratigraphically and petrographically by the author (Crook, 1961 a, D, c). An outline of their stratigraphic subdivision is presented in Table 1. In the Tamworth-Nundle district, and westwards the two groups ex- hibit a depth sequenceof diagenetic minerals (Crook, l96lc), in which three diagenetic facies are represented-the laumontite, the prehnite- pumpellyite, and the albite-epidote.In addition, veins bearing calcium- aluminium silicatesare common in the sequence,seventy-odd having beenexamined. These are describedherein. Optical data, incorporatedin Table 2, have been obtained from min- eral fragments in most cases,although thin sectionswere utilized for quartz-rich veins (R96tt-R970). Refractive indices were measuredby the immersionmethod, using Cargilleoils checkedon an Abbe refractometer. Accuracy is *0.002 for values below 1.600 and generally somewhat poorer for values above this. Specimen numbers of the W-series are the author'sfield numbers(series KCW. ... /56,57 or 58). Thoseof the R-seriesare University of New England collection numbers (old series). AII material is housed in the University of New England. * Now at Geology Dept., Australian National University, Canberra, A.C.T., Australia. tolT 1018 KEITH A. W. CROOK ..EUNDARM . URALLA KEI'FS€Y a o PRT MCq)Are Vr I ll \ tl t'. t16 IIf :\ lo 20 30 40 *oE h nkls Frc. 1.Locality map (geologicaldata from Voisey, 1959). The veins occur in several different ways: (o) straight or irregular macroscopicor microscopic veins apparently unrelated to any structural features of the rock. (b) joint fillings (c) bedding veins (d) in fault planes, along the margins of dykes which occupy faults, or in shear zonesin dykes. Those of type (a) are the earliest, being cut by joints. As will be shown elsewhere,jointing was the earliest structure formed during deformation VEIN MINERALS FROM NEW SOUTH WALES 1019 Tasrn 1. Srnnrrcnlpmc SusorvrsroNsor r:nr TLuwoRTHAND Pe.rnv Gnoups Eastern and Southem Regions Westem and Northern Regions (not preserved) "Lower Kuttung Group" (CK) -l 3 -4a -s -Boiling 7 9 Down Sandstone Member P_ ; (Clbs) .. n- F o 'ia;Y s R- E E s- j *d E E r'3 p. O B HX U_ Fr o .;F V_ FF -Gowrie Member (Clgs) tsl Eg Va- Sandstone -b w- -8 X- -9 Y- -10 z, -Turi Graywacke Member (Clt) -Benama Graywacke Member (Clbg) -Garoo Conglomerate Member (Clgc) -Wombramurra Formation (Clw) -Scrub Mountain Conglomerate Mem- -Scrub Mountaiu ConglomerateMem- ber (Cls) ber (Cls) -Hyde Graywacke Member (Clh) -Kiah Limestone Member (Duk) Upper Devonian Baldwin Formation (Dub) Baldwin Formation (Dub) Yarrimie Formation (Dmy) Yarrimie Fomation including Middle s Levy Graywacke Menber (Dmlg) Devonian Silver Gully Formation (Dms) Silver Gully Formation (Dms) il wogarda Argillite (Dlw) Drik-Drik Formation (Dld) Seven Mile Fomation (Dls) H F Cope's Creek Keratophyre (Dlc) il. Lower Pipeclay Creek Eormation (Dlp) Devonian ts Hawk's Nest Beds (Dh) Stratigraphic F position unknown) of the area, pre-dating the folding. Thus the joint fillings (b) post-date type (o). The bedding veins (c), which are clearly later than the joint fill- ings, where intersections occur, are probably related to the folding' as re- lief of load pressurewould be necessaryfor material to be depositedalong beddingplanes. The veins of type (d.) arc probably also related to the folding. In an- other place the faults and shearsin which they occur will be shown to be related to the folding or to be later than it. Veins of type (d) may there- fore be consideredas roughly contemporaneouswith those of type (c). 1020 KEITH A. W. CROOK Ttnt-t 2, Pnopnnrrrs ol Vrrn Mrrvnner,s Forma,tion CO, Laumontite Stilbite QtarLz V"in Prehnite p (present) rYPe Epidote Position ZLc aa P B m (minor) d 1.658 1.516 13' c 1.520 10' b3 c 1658 1520 - b 1.494 1.503 b 1.494 1.505 _l 1.658 1.515 36" 1.658 1.658 1.492 1.505 1 658 d 1 658 and also anom biaxialF:1.632; r:1.640 (strained) d 1 658 1.517 50' d 1.658 1.489 1.503 1.517 36" b 1.489 1 50s D 1.489 1.503 a 1.764 p W282a Cls below Clps d 1.517 46" R965 Cloc? pres. 1.620 W33l Cli above Ctbs d 1 658 WJ40b Cl6e i .658 t.764 p W3sJa Clbi 1.620 t) W369 Clg-(low) v. mlnor p W402 Dmy 1.682 r) W487 Clw a 1.658 1.621 p W489 Clw a 1.748 p W498 Clw a 1.753 I) a p b 1.514 41" 1.489 1.505 c 1.517 4r' b 1.489 1.504 1.517 41" c 1.658 1.517 16";43' I .658 a 1.658 p 1.658 | .517 36' d p c 1.517 16';36' b3 c I .658 I 517 26";53" b I 658 1.517 16" 1.490 I .505 d I 6s8 d 1 517 49" 1 658 1.62r 1.658 1.5r7 16";42" 1.489 1.501 d 1 658 r.5r7 45' 1.634 p c p W876 Clps d /1.6s8 11.704 W898 Cls 1.621 W909 Cle below Cls D 1 658 W917 Dms a 1.658 W932 Dmy - 1.517 40" W941 Dlw 1.750 W949 Cle below Clpp- -' d 1.658 1 517 45' R967 DT (?Dms) a3 1.658 1.750 W956 DT (?Dms) ai R968 DT (?Dms) a 1.658' present present p W1051 Dub 1.658 1.517 43" W1098 Dmy 1.658 R970 Duh a 1 .658 minor present p W1106 Dub b 1.489 1.506 W1114 Cls above Duk p W1116 Cls sl. above Duk I 615 p W1141 Clpv? - 1.056 W1142 Cls below Cls d 1.658 1 517 41" W1143 Cls below Clnr, - 1.658 1.517 45' 1.489 1.505 W1147 Clpz - 1.658 1.751 p W1l47a Clp2 t.752 1.617 p W1147bDms - 1.658 Wl151 Clw a 1.615 p w1155 Dld ?altered-agg.pol. n:1 53 W1167 Clg below Clpro a 1.755 p r "-" indicatesdata on tyDe not recordedia 6eld-book. 2 Also contains cblorite and muscovite. E Axinite presentas follows: R967,6- 1.680:W956. d: j.684. Heulanditepresenr in W 111.6:1.502. W700.d J1.505:W I I 14.d:1.497. Pumpellyitepresent in R965, and in RsOO;p';t.osO-t.zoO. VEIN MINERALS FROM NEW SO\]TH WALES IO2I MrNnn.A.rocv The following mineralshave beenencountered in the veins,and will be discussedin order: carbonates epidote Iaumontite axinite stilbite chlorite heulandite muscovite prehnite quartz pumpellyite albite bytownite Carbonates:Calcite is by far the most common carbonate' and is re- markably pure. It is usually white en masse'and colorlessand trans- parent in crushed fragments. Thirty-seven determinations give c,l :1.658+0.002. In one case(W1604) optically anomalouscarbonate oc- curs with calcite' This shows 0:I.632+o.002, 1:1'640*0'002 and 2V(-) ca. !0o.It has wavy extinction, and the anomalousoptics are ap- parently due to strain. In only two caseshave carbonatesother than calcitebeen encountered' These are W876 from Member 9 of the Pyramid Hill Arenite (a brown carbonate)and W402 from the Yarrimie Formation' Thesehave W876 o: l.7M + 0.003(occurswithcalcite) W4O2o:7.682+0.002. Both are uniaxial negative.The refractive index determinationssuggest dolomite. Carbonateoccurs throughout the sequence,having been encouptered as far down as the Silver Gully Formation. Laumontite is also-widespread,usually in bedding veins or fauits. It oc- curs as silky white columnar prismatic crystals, showing good cleavage' and often forms acicular clumps. It is usually associatedwith calcite. Twenty-threedeterminations give P:t.5I4 to 1.520,2V(-) ca.30o. The extinction angle (ZLc) vafies between 10" and 53o. Usually the central parts of grains give Iower values, about 16o' whilst the margins give values about 42o.The junction betweenthe optically differentma- terials is irregular, but sharp. At times the two types of material are ar' ranged so as to simulate complex twinning, giving a patchy extinction' This variation in optical properties has been discussedby Coombs (1952) with whosedata the presentdata are in good agreement.He has shown that the variation is due to the Iaumontite becoming modified to leonhardite by loss of water.
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