Application of Skarn Deposit Zonation Models to Mineral Exploration

Most large skarn deposits are zoned in both space and time relative to
associated intrusions. Zonation occurs on scales from kilometers to micrometers,
and reflects infiltrative fluid flow, wallrock reaction, temperature variations,
and fluid mixing. The most spectacular examples of skarn zonation usually occur
at the skarn-marble contact, where transitions between monomineralic bands can
be knife sharp. Other small-scale examples occur in zoned veins and individual
mineral crystals. Although, visually striking and scientifically interesting, in
mineral exploration these small-scale variations are less useful than deposit-
or district scale zonation. In most skarn systems there is a general zonation
pattern of proximal garnet, distal pyroxene, and vesuvianite (or a pyroxenoid
such as wollastonite, bustamite, or rhodonite) at the marble front. As well,
individual skarn minerals may display systematic color or compositional
variations within the larger zonation pattern. Such patterns are reviewed for 14
well-studied examples of Cu, W, Sn, Au, and Zn-Pb skarns. In addition, many
deposits have endoskarn or other alteration of the associated intrusion, and
recrystallization or other subtle changes have occurred in the surrounding
wallrocks. Copper skarns, such as Mines Gaspé in Quebec and Big Gossan in Irian
Jaya, have high ratios of garnet:pyroxene and are zoned outward from the
intrusion, to garnet, to pyroxene, to massive-sulfide replacement and vein
deposits. Garnets in Cu skarn are Fe-rich and change from dark red-brown near
the intrusive contact to paler brown, green, or yellow in distal locations.
Pyroxenes in Cu skarns are pale and diopsidic near the intrusion, and become
darker and more Fe- and Mn-rich away from the intrusion. Tungsten skarns, such
as Salau and Costabonne in France and Pine Creek and Garnet Dike in California,
have intermediate ratios of garnet:pyroxene, are more extensive vertically and
along strike than perpendicular to the intrusive contact, and have zonation
patterns commonly complicated by overprinting of metamorphic lithologies. In W
skarns, garnet is commonly subcalcic and the pyroxene is Fe-rich, reflecting
particularly reducing wallrocks or great depth of formation. Tin skarns, such as
Dachang in China and Moina in Australia, also can have subcalcic garnet and
Fe-rich pyroxene, but this reduced mineral assemblage typically is due to an
association with reduced S-type granites. Tin skarns differ from most other
skarn types in having a late greisen stage that may replace earlier Sn-bearing
calc-silicate minerals, thus liberating Sn to form cassiterite. Many high-grade
Au skarns, such as Hedley in British Columbia and Fortitude in Nevada, have low
ratios of garnet:pyroxene and are associated both with reduced plutons and
reduced wallrocks. Goldrich zones occur in Fe-rich, pyroxene-dominant, distal
skarn. Zn-Pb skarns, such as the Yeonhwa- Ulchin district in Korea and Groundhog
in New Mexico, have low ratios of garnet:pyroxene and generally form distal to
associated intrusions. These skarns also are zoned from proximal garnet to
distal pyroxene and pyroxenoid (bustamite-rhodonite), with significant zones of
massive sulfides within and beyond skarn. Manganese enrichment of most mineral
phases, particularly pyroxene, is characteristic of distal zones. Fundamental
controls on skarn zonation include temperature, depth of formation, composition
and oxidation state of associated plutons and wallrocks, and tectonic setting.
Most W skarns form at relatively great depth, 5 km to 20 km, with extensive
high-temperature metamorphic and metasomatic mineral assemblages. In contrast,
most other skarn types are relatively shallow, <10 km and mostly <5 km,
with limited, lower temperature metamorphic aureoles. Differences in oxidation
state correlate well with different skarn zonation patterns, particularly
garnet:pyroxene ratios and compositions, and can be used in both classification
of and exploration for skarn deposits. Zonation models, especially where
quantified, can be used predictively in exploration both for known and blind
Keywords: Skarn deposits, Skarn zonation, Mineral exploration
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Summary: The Geological Society has its own quarterly journal called Exploration
and Mining Geology, for the publication of Canadian and international papers on
applied aspects of mineral exploration and exploitation, including mineral
deposit geology, geochemistry, and geophysics, mining geology, mineral resource
appraisal and estimation methods, environmental geology, and case histories. The
editor of the journal is Jeremy P. Richards
Publication: Exploration & Mining Geology
Issue: 2
Volume: 6
Year: 1997
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<BODY>The mechanism by which stratiform ore deposits of PGE (platinum-group
elements) are laid down in ultramafic igneous complexes is not completely clear.
Early studies by the author and coworkers on numerical analyses of the
convective cooling of low-Rayleigh-number magma chambers...
Publication: Exploration & Mining Geology
Author(s): ALAN RICE: Departments of Geology and Physics, Rhodes University, Grahamstown 6140, South Africa
Keywords: PGE, Ultramafic igneous complexes, Magma chambers, Suspended
Issue: 2
Volume: 6
Year: 1997
Web Page
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<META name=GENERATOR content="MSHTML 9.00.8112.16440"></HEAD>
<BODY>The Campo Morado precious-metal-bearing, volcanogenic massive sulfide
deposits occur in a lower Cretaceous, bimodal, calc-alkaline volcanic sequence
in a major northerly trending belt in the Guerrero Terrane in northeastern
Guerrero, Mexico. During upper Cretaceous to Early...
Publication: Exploration & Mining Geology
Author(s): JIM OLIVER, JOHN PAYNE and MARK REBAGLIATI: Farallon Resources Ltd. Vancouver, British Columbia, Canada V6C 2V6
Keywords: Precious metals, Sulfide deposits, Volcanic, Mexico, Minerals
Issue: 2
Volume: 6
Year: 1997
Summary: Economic Mn-oxide ore deposits of commercial grade occur in the Rhodope massif near Kato Nevrokopi in the Drama region, Northern Greece. The Mn-oxide mineralization has developed by weathering of continental hypogene rhodochrosite-sulphide veins. The vein mineralization is confined by tectonic shear zones between marble and metapelites, extending laterally into the marble as tabular, pod or lenticular oreshoots (up to 50 m ?? 20 m ?? 5-10 m). Supergene oxidation of the hypogene mineralization...
Publication: Exploration & Mining Geology
Author(s): M.K. NIMFOPOULOS: Institute of Geology and Mineral Exploration (IGME), 546-26 Thessaloniki, Macedonia, Greece; R.A.D. PATTRICK: Department of Earth Sciences, The University of Manchester, Manchester M13 9PL, England, U.K.; K.M. MICHAILIDIS: Department of Mineralogy-Petrology-Economic Geology Aristotle University, 540-06 Thessaloniki, Macedonia, Greece; D.A. POLYA and J. ESSON: Department of Earth Sciences, The University of Manchester, Manchester M13 9PL, England, U.K.
Keywords: Ore deposits, Geology, Geochemistry, Vein mineralization, Supergene oxidation
Issue: 2
Volume: 6
Year: 1997
Summary: The Croft diorite in central England belongs to a suite of Caledonian igneous rocks collectively known as the South Leicestershire diorite complex. Although the intrusions occupy separate outcrops, they are linked at depth to form a single pluton, buried beneath a cover of Triassic sediments (Le Bas, 1972; 1982, Allsop and Arthur, 1983). Both the Caledonian diorites and the overlying sub-Triassic unconformity have been affected by a complex history of alteration and mineralization which can...
Publication: Exploration & Mining Geology
Author(s): K. PEARSON and C.A. JEFFREY: Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH, U.K.
Keywords: Caledonian igneous rocks, Intrusions, Deuteric effect, Sodic enrichment, Laumontite veins, Analcime veins, Calcite veins, Mineralization
Issue: 2
Volume: 6
Year: 1997
Summary: Detailed petrographical and geochemical studies have been carried out on the igneous and sedimentary rocks in the Omai area, part of the Paleoproterozoic Barama-Mazaruni greenstone belt, Guyana. The stratigraphic succession at Omai begins with basalts, associated with mafic ultramafic intrusives and poorly-sorted conglomerates; these are overlain by andesites and quartzfeldspar porphyries, with pelites and tuffaceous sediments at the top. The volcanic-sedimentary succession was intruded by a...
Publication: Exploration & Mining Geology
Author(s): GABRIEL VOICU, MARC BARDOUX, LUC HARNOIS: Département des Sciences de la Terre, Université du Québec à Montréal, Montréal, QC, Canada H3C 3P8 and ROBERT CRÉPEAU:
Omai Gold Mines, Georgetown, Guyana, South America
Keywords: Petrographical studies, Geochemical studies, Guyana, Basalts, Mafic-ultramafic
intrusives, Conglomerates
Issue: 2
Volume: 6
Year: 1997
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