Heavy minerals can contain potentially economic amounts of
metals as both matrix and trace constituents. Such minerals appear
as unconsolidated black sands on the continental shelf off southwest
Oregon and along the Oregon coast. Two diverse energies are considered in this investigation. Environmental energy of the depositional
regimen, Part I; energy involved in crystallization of transition
metals from a magma, Part III. In Part II, an analytical scheme for
the evaluation of opaque oxides is proposed, and an examination of the
results as applied to two samples is presented.
Part I
The unconsolidated black sands on the Oregon continental margin
have been profoundly affected by tectonic uplift aid by cyclic erosive
transgression and regression. Progressive enrichment in heavy
minerals from the Klamath Mountains has apparently occurred during
each glacio-eustatic regression of the Pleistocene seas, each regression
a period of intensified erosion and sediment transport. Subsequent
erosive transgressions selectively sort and redistribute these
heavy minerals into paralic beach and nearshore deposits. Uplift of
the coast and shelf implies that the heavy minerals were reworked
during the Holocene transgression into concentrations of greater
extent and higher ore tenor than relict deposits of earlier transgressions
in upraised Pleistocene terraces. Extrapolation of ore
reserve values from the terraces by "Mirror Image" concepts might
seriously underestimate the potential of offshore deposits. Offshore
heavy mineral concentrations should be coincident with observed
submarine terraces.
Part II
An analytic scheme was developed to investigate opaque oxides
in two samples; one from the Pleistocene terraces; the other from
near the present shelf edge. Analyses involving X-ray diffraction
techniques, atomic absorption and neutron activation established the
mineralogy and elemental distribution in magnetically separated diagnostic
splits. Chrome spinel, ilmenite and magnetite comprise the
opaque oxide fraction in both samples.
Correlation studies of these analyses suggest:
(1) Chromium is a matrix metal of chrome spinel and is diadochic
into magnetite.
(2) Iron appears in all opaque oxides and in increasing amounts
with increasing magnetic susceptibility.
(3) Titanium is a matrix metal in ilmenite, and diadochic into
chrome spinel and magnetite.
(4) Nickel and ruthenium are diadochic into and correlated to the
spinel structure; i.e. to chrome spinel and magnetite.
(5) Osmium appears to be correlated to chromium.
(6) Zinc is limited to spinel in these samples.
Part III
Goldschmidt's and Ringwood's criteria for diadochy often fail to
explain the distribution of the transition metals because crystal field
effects are not considered. Favored d[superscript n] configurations, e.g. octahedrally
coordinated, low spin d⁶ cations in the spinel minerals, result
in shortened interatomic distance and significantly strengthened
cation-ligand bonds, possibly affecting the distribution of such metal
cations.
The octahedral site preference energy parameter (OSPE) has
been used to explain distributional behavior of the first (3d) transition
series metals. OSPE calculations for four low spin d⁶ cations -
Co(III), Ru(II), Rh(III), and Pt(IV) - give significantly high values for
this parameter.
High OSPE valued transition metal cations possibly form stable
proto-mineral oxide complexes in the magma which persist through
crystallization. These associations predetermine the enrichment of
transition metals in oxide minerals and act as nuclei during cooling
and solidification.
Subduction of oxidized and hydrolyzed near-surface rocks down
a Benioff zone provides progressively higher Eh in the magma, a
variety of cation oxidation states, and water for sepentinization of
ultramafic rocks. The distribution of the platinum metals in a
strongly reducing magma environment should be different than in the
oxidizing magma proposed for the Klamath ultramafics.
The OSPE parameter offers an explanation for the observed
distribution of platinum group metals in spinel minerals from this
investigation, in chromites from Uralian dunitic massifs and the
Stillwater complex; and of iridium from the Great Lake Doleritic
Sheet, Tasmania. Chrome spinel from Oregon had twice the concentration
of ruthenium, and one-third the amount of osmium as similar
Uralian chromite deposits. The first significant concentration of
ruthenium in magnetite is herein reported recommending continued
research into the platinum metal distribution in southwest Oregon. / Graduation date: 1972
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29078 |
| Date | 08 February 1972 |
| Creators | Bowman, Kenneth Charles Jr |
| Contributors | van Andel, Tj. H. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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