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Abstract

Comparison of the 100Zn/(Zn + Pb) ratio ( "zinc number") of various styles of
mineralization in the Mt. Read Volcanics of Tasmania indicates that volcanogenic
massive sulfide deposits have a restricted range of mean values (64 to 77) and low
standard deviations (less than 15) while other mineralization styles have a broader, but
lower, range of mean values (39 to 61) and higher standard deviations (greater than
26).
The consistency of the zinc number, along with the Pb vs. Zn plots, suggests
that zinc and lead were saturated in the metal deficient (mΣmetal< mH2S) hydrothermal
fluids that deposited Rosebery and Hellyer. Trends in the zinc number between massive
sulfides in the Mt. Read Volcanics indicate that concentrations of zinc and lead in the
footwall volcanic source rocks did not control the zinc number of the deposits. The
saturation of zinc and lead in mineralizing fluids may control the zinc number of most
Phanerozoic volcanogenic massive sulfide deposits, but low concentrations of lead in
the footwall volcanics of Cu-Zn type massive sulfide deposits probably control the zinc
number for this class.
The low means and high standard deviations of Cambrian vein deposits in
the Mt. Read Volcanics, and Ordovician and Devonian deposits of the Dundas Trough,
may be explained by a lack of zinc- lead saturation or by different complexing in the
relevant hydrothermal fluids.
The characteristic zinc number of volcanogenic massive sulfide deposits can
be used to distinguish these deposits from other mineralization types in the Mt. Read
Volcanics. Effective use of this simple technique requires a reasonable number of anomalous samples (minimum = 15) and an unoxidized sample medium (drill samples
are preferable). In combination with geology and lead isotopes, the zinc number
provides an excellent early screening of prospects.

Item Type:	Report (Technical Report)
Authors/Creators:	Huston, DL and Large, RR
Publisher:	University of Tasmania
Additional Information:	© University of Tasmania 1986
Item Statistics:	View statistics for this item

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