摘要:

K‐Ar ages of biotite and hornblende from undeformed granodiorite plutons and of slaty and phyllitic rocks, ranging from prehnite‐pumpellyite metagreywacke to greenschist fades, have been determined in an attempt to define the age of orogenesis in the eastern part of the Nambucca Slate Belt. The plutons have K‐Ar ages of 226–227 m.y. (biotite) and 228–231 m.y. (hornblende) that provide a younger age limit for deformation. The lower grade metamorphic rocks yield a range of ages including some comparable with the depositional age of the rocks as indicated by fossils. Rocks of pumpellyite‐actinolite and greenschist facies give a more coherent group of ages which suggest orogenesis at about 250–255 m.y. Specimens of these latter rocks that have been affected by a later structural episode than that during which slaty cleavage formed, yield slightly older ages, which may result from the inclusion of minor amounts of environmental excess40Ar.

ISSN:0016-7614    

DOI:10.1080/00167617908729074

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

Palynological studies and lithologic interpretations from logged water bores and petroleum exploration wells in the northeastern Eromanga Basin show that: (a) the mid‐Jurassic to Lower Cretaceous rock sequence including Hutton Sandstone‐Injune Creek Group‐Hooray Sandstone is recognised in the southern and western parts of the area previously mapped as Ronlow Beds; (b) these rock units thin northeastwards, where they merge, each in different places, into an apparently indivisible quartzose sandstone unit for which the name Ronlow Beds is retained; (c) the Cadna‐owie Formation, which overlies the Hooray Sandstone in the subsurface of the southwestern part of the study area, is missing in a broad zone along the present‐day basin margin, where it is thought to have been at least partly eroded: (d) the regional palynological record includes the interval from mid‐Jurassic unit J4 to the Early CretaceousMurospora floridaZone, but is incomplete. Late Jurassic unit J6 is missing, and so are certain Neocomian intervals within theMurospora floridaZone in some areas along the basin margin.

ISSN:0016-7614    

DOI:10.1080/00167617908729075

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The Woodlawn zinc‐lead‐copper deposit is one of a number of stratabound volcanogenic base‐metal deposits in the eastern part of the Lachlan Fold Belt. These deposits are commonly bandned and chemically zoned. They are copper‐rich at the base and lead‐zinc‐(barium)‐rich at the top. Alternatively, discrete copper‐rich, lead‐zinc‐rich and barium‐rich bodies may be developed. Oxide facies variants have been recognised at a number of localities. The deposits were formed in or adjacent to volcanic rifts during the Late Silurian. The Woodlawn deposit is located within the Captains Flat‐Goulburn Synclinorial Zone within a sequence of quartz‐feldspar porphyry, agglomerate, tuff, tuffaceous shale and black shale.

ISSN:0016-7614    

DOI:10.1080/00167617908729076

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The Woodlawn Deposit comprises an outcropping, composite body consisting of one large and several smaller lenses of polymetallic massive sulphides with an associated zone of copper mineralization, and several separate non‐outcropping bodies of massive sulphides occurring downdip in the same stratigraphic sequence.

ISSN:0016-7614    

DOI:10.1080/00167617908729077

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The main Woodlawn ore lens is a polymetallic, massive sulphide deposit’ with pyrite the major constituent, variable sphalerite, galena and chalcopyrite, and minor arsenopyrite, tetrahedrite‐tennantite, pyrrhotite and electrum. The silicate gangue minerals are chlorite, quartz, talc and sericitic mica. Other mineralization in the vicinity consists of footwall copper ore in chlorite schist and several smaller massive sulphide lenses. The predominant country rocks are felsic volcanics and shales, with abundant quartz, chlorite and mica, and talc in mineralized zones.

ISSN:0016-7614    

DOI:10.1080/00167617908729078

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The volcanogenic Woodlawn Cu‐Pb‐Zn sulphide mineralization occurs within a low‐grade metamorphosed sequence of Middle to Upper Silurian felsic volcanics and fine‐grained sedimentary rocks. Studies on a total of 234 rock samples from diamond drill holes have delineated zones of hydrothermally altered rocks extending more than ∼500 m laterally from the main ore lens, at least ∼100 m into the foot wall and up to ∼200 m into the hanging wall. These altered rocks contain virtually no remnants of primary feldspars and ferromagnesian minerals, and they are variably chloritized, sericitized and silicified. Chlorite and disseminated sulphide minerals are most abundant in zone I, a restricted zone of intense alteration immediately around the main ore lens, whereas sericitic muscovite is most abundant in the relatively extensive zone II, further from the ore. Silicification is also a feature of volcanics well beyond the limits of observed phyllosilicate‐rich alteration zones. Chemical changes within the hydrothermally altered rocks include major enrichment of Fe, Mg, S, Si and H2O, more sporadic enrichment of Ag, Ba, Bi, Cd, Cu, Mn, Pb, Sn and Zn, and major depletion of Ca, Na and Sr. K is depleted in zone I and shows considerable variation, but no overall depletion or enrichment, in zone II.

ISSN:0016-7614    

DOI:10.1080/00167617908729079

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The presence of base‐metal mineralization at Woodlawn was first recognised early in 1968 when a roadside reconnaissance geochemical sampling survey, conducted over felsic volcanic rocks in the Goulburn‐Tarago area, encountered anomalous B horizon soils containing up to 200 ppm Cu, 800 ppm Pb and 300 ppm Zn. Regional soil thresholds have been determined at 50 ppm Cu, 90 ppm Pb and 50 ppm Zn. Chip samples from the subsequently located gossan revealed up to 2000 ppm Cu, 8000 ppm Pb and 2000 ppm Zn, 500 ppm Sn, 25 ppm Ag and 3000 ppm As.

ISSN:0016-7614    

DOI:10.1080/00167617908729080

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

34S/32S ratios have been measured in a suite of samples from the stratabound, volcanogenic massive sulphide deposit at Woodlawn, N.S.W.34S values for the sulphides vary as follows: in the ore horizon, pyrite +6.7 to +9.2%. (mean +8.1‰), sphalerite +5.2 to +8.6‰. (mean+6.9‰),chalcopyrite +6.4 to +7.0‰ (mean +6.7‰) and galena +2.8 to +5.5‰ (mean +4.4‰); in the vein mineralization, the host volcanics—pyrite +8.7 to +11.4%. (mean +9.8‰), sphalerite +7.8 to + 10.3‰ (mean +9.2‰), chalcopyrite; +8.8 to +10.1‰ (mean +9.2‰) and galena +6.9 to +7.2‰ (mean +7.1‰). Barite from the upper ore horizon levels has an isotopic composition of +30.0‰, consistent with its having originated from Silurian ocean sulphate. The general order of34S enrichment in the sulphides is pyrite > chalcopyrite∼sphalerite > galena. Isotopic fractionations in the systems galena/sphalerite/pyrite and chalcopyrite/pyrite indicate an equilibration temperature of 275–300°C. This temperature is considered to represent that of sulphide deposition.

ISSN:0016-7614    

DOI:10.1080/00167617908729081

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

In the massive sulphide ore of the Woodlawn Pb‐Zn‐Cu deposit, lead isotopic ratios of pyrite, galena, sphalerite, and chalcopyrite are uniform (206Pb/204Pb 18.089,207+Pb/204Pb 15.605,208Pb/Pb20438.106) and are the same as the initial lead ratios in pyrite from the host volcanics. Pyrite from the footwall appears to be more radiogenic in206Pb and208Pb, and to have lower Pb concentrations than those in the hanging wall. Initial lead ratios in the whole rock volcanics are the same as those in the ore, thus suggesting a common source for the lead. Lead isotopic data for the gossan minerals are the same as for the primary sulphides; this demonstrates that no isotopic fractionation or contamination by radiogenic lead occurred during oxidation of the primary ore.

ISSN:0016-7614    

DOI:10.1080/00167617908729082

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The structures across the Lambian Unconformity near Taralga show evidence of two, and possibly three, significant episodes of folding. The first, Early to Middle Silurian folding is poorly defined, but may be responsible for initial dips that are reflected in the more complex deformation patterns in the Late Ordovician than in the overlying younger rocks. The second, mid‐Devonian folding produced upright folds trending 10° west of north, and the last, latest Devonian to Early Carboniferous folding produced the meridional Cookbundoon Synclinorium and the regional cleavage. No cleavage was associated with the first two episodes of folding in the area studied. The angular discordance across the Lambian Unconformity caused by mid‐Devonian folding is much greater than in the northeastern Lachlan Fold Belt, and reflects the increasing intensity of mid‐Devonian folding southward. The tight, slightly overturned profile of the Cookbundoon Synclinorium reflects an intensity of latest Devonian to Early Carboniferous folding similar to that found in the northeastern Lachlan Fold Belt, but the intensity of this folding decreases further south.

ISSN:0016-7614    

DOI:10.1080/00167617908729083

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor