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Hellyer Stringer Zone Project. Progress Report No. 1 (CODES publication 17)


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Gemmell, JB 1988 , Hellyer Stringer Zone Project. Progress Report No. 1 (CODES publication 17).

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The alteration zone underlying Hellyer is larger in size and extent than commonly reported for volcanogenic massive sulphide deposits and has consistent alteration mineral zonation with Archean deposits and deposits hosted in mafic volcanics. Alteration within the siliceous core of the feeder system consists of intensive silicification down to a depth of 350 m below the massive sulphide. The silicification is underlain by chloritic alteration to the known extent of the alteration system (555 m).

Eight stages of veining have been determined in the alteration zone, these include one stage of pre-mineralisation, three stages of syn-mineralisation, and four stages of post-mineralisation veining. The most
abundant veins are related to the mineralising processes
and contain significant quantities of base-metal and iron
sulphides. The identification of the syn-mineralisation
veins within areas of intense alteration is a good
exploration target.

An analysis of metal zoning in the stringer zone
indicates the presence of three feeder systems within
the alteration pipe. The central feeder is located in the
middle of the deposit (10720 N/l0850 N) with a second
feeder system to the south (l0500N) and a third feeder
system is weakly developed under the far northern
portion of the ore body (10950N). The alignment of the
three hydrothermal systems under the massive sulphides
is not related to the Jack fault and may be of significance
for regional exploration.

Fluid inclusion measurements indicate that the fluid responsible for the formation of the syn-mineralisation
veining are consistently of high temperature (280-350°C) but of varying salinity. Stage 2A quartz-pyrite-carbonate veins have high salinities (12 - 24 equiv. wt % NaCI) while Stage 2B base-metal-rich sulphide veins have very low salinities (<3 equiv. wt % NaCI). The high temperature-low salinity data are similar to the stockwork siliceous ores of the Kuroko deposits.

Carbon and oxygen isotope analyses of carbonate minerals reveal slight differences between the various vein stages and the chlorite-carbonate alteration, but these differences are minor. The carbon and oxygen data suggests, even though there are differences in the
time of precipitation of carbonates in the various syn- and
post-mineralisation veins and the chlorite-carbonate
alteration, a similar source (seawater or modified
seawater) for both the carbon and oxygen in carbonate
minerals throughout the Hellyer stringer system.

Item Type: Report (Technical Report)
Authors/Creators:Gemmell, JB
Publisher: University of Tasmania
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