Abstract

The Munni Munni Complex is a boat-shaped layered intrusion, divided into a lower ultramafic 'keel', up to 1850 m thick, overlain by a gabbroic sequence at least 3000 m thick. The top of the ultramafic series is marked by a 20-80 m thick porphyritic websterite zone (PWZ), that extends laterally to form a 200 m thick layer of pyroxenite along the walls of the intrusion. Platinum-group element (PGE)-enriched disseminated sulphides occur within the top 20 m of the PWZ unit along its entire exposed strike length, with maximum total PGE grades up to 8 ppm over 500 mm widths. The PWZ marks a pronounced discontinuity in mineral composition trends within the intrusion, between uniform relatively high Mg# and Cr-rich pyroxenes in the main part of the ultramafic series, to gabbroic cumulates showing a monotonous trend of declining Mg# due to closed system fractionation in a large chamber. The Cr2O3 content of cumulus augite shows a dramatic drop from about 0.2% to less than 0.05% over less than 4 m near the top of the PWZ. Disseminated cumulus sulphides are abundant within an interval from 5 m above the gabbro contact to 15 m below it. Two sulphide components are present. The first is a relatively PGE-poor component, characterized by coincidence of peak Cu, Ni, S and PGE abundances. The second is a variable composition component, strongly PGE enriched at the base and depleted at the top, characterized by systematic offsets between the peak PGE and Cu abundances. The 'offset' sulphides always occur above the 'coincident' sulphides, and their first appearance corresponds to the sudden drop in Cr2O3 content of clinopyroxene within the PWZ. The coincident sulphides are interpreted to have formed by batch equilibration of sulphide liquid droplets during the magma mixing event that produced the PWZ. The offset sulphides formed subsequently by fractional segregation and gravity settling of sulphide liquid droplets from a stagnant hybrid melt layer dominated by the gabbroic component. The observed lateral distribution of PGE-rich sulphides in the PWZ is inconsistent with derivation of PGE from trapped liquid in underlying cumulates and provides strong evidence for the existence of primary PGE-enriched cumulus sulphide liquid.
Google map showing geographic bounding box with values North bound -20.5 East bound 117.6 West bound 116.0 South bound -21.5
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Product Type/Sub Type

dataset - External Publication - Scientific Journal Paper

Constraints

license
Creative Commons Attribution 3.0 Australia Licence

IP Owner

Commonwealth of Australia (Geoscience Australia)

Author(s)

Date (publication)

1992

Product Type

dataset

Topic Category

geoscientificInformation

Keywords

External Publication
Scientific Journal Paper
Earth Sciences

Resource Language

English

Resource Character Set

utf8

Resource Security Classification

unclassified

Geographic Extent

North bound
-20.5
East bound
117.6
West bound
116.0
South bound
-21.5

Lineage

Unknown

Digital Transfer Options

onLine

Distributor

Role
distributor
Organisation Name
Geoscience Australia
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address

Metadata File Identifier

a05f7892-faa1-7506-e044-00144fdd4fa6

Metadata Standard Name

ANZLIC Metadata Profile: An Australian/New Zealand Profile of AS/NZS ISO 19115:2005, Geographic information - Metadata

Metadata Standard Version

1.1

Metadata Date Stamp

2010-11-16

METADATA SECURITY CLASSIFICATION

unclassified

Metadata Contact

Role
pointOfContact
Organisation Name
Geoscience Australia
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address
Related Links
For information on acquiring this product,
please contact the Geoscience Australia Sales Centre via:

fax:
+61 2 6249 9960; or
phone:
1800 800 173 (within Australia);
 
+61 2 6249 9966 (outside Australia).

Please note that support hours are 9 am to 5 pm weekdays