Electron spin resonance (ESR) dating

Rutile solubility in H2O, H2O–SiO2, and H2O–NaAlSi3O8 fluids at 0.7–2.0 GPa and 700–1000 °C: Implications for mobility of nominally insoluble elements

Titanium mobility in metamorphic systems: a review

Titanium is a dispersed lithophile element commonly regarded as chemically immobile at sub-magmatic temperatures. However, a growing number of field studies demonstrate that Ti is somewhat mobile in certain environments. This review examines the current state of knowledge concerning the mobility of Ti during alteration and metamorphism of crustal rocks. Also considered are relevant Ti-oxide solubility data from experiments and determinations of Ti concentrations in natural waters. Where Ti mobility is well documented, its length scale is ≤ 10 m. However, Ti may move greater distances in deep crustal shear zones. The solubility of Ti-oxides in geologic fluids is strongly temperature dependent

Extensive pyrite-bearing, auriferous cobble and boulder conglomerates are present in the basal 30 in of the Mississagi Formation in Pardo and Clement Townships, Ontario, Canada. The sedimentology of the conglomerates, combined with regional geology, indicates limited fluvial transport in a gravel bed braided river with local hyperconcentrated flows, with material derived from a highly restricted catchment area. Postdepositional overprinting of the conglomerates is related to the Penokean orogeny at 1.85 to 1.5 Ga and alkali metasomatism at similar to 1.7 Ga. Several pyrite varieties, including detrital and postdepositional recrystallized and altered grains, are present in the conglomerates. Detailed in situ laser ablation inductively coupled plasma-mass spectrometry (LA ICPMS) analysis of pyrite revealed that the gold in the deposit is intimately associated to large detrital pyrite grains, as "invisible" Au, with lesser amounts of free gold. Postdepositional pyrite and pyrite overgrowths have very low Au content. Elements such as Pb, Bi, Sb, Te, Ag, and Hg, together with Au were mobilized during hydrothermal alteration and dissolution of detrital pyrite grains. Small-scale transport and reprecipitation formed part of the postdepositional pyrite and free gold in immediate contact with postdepositional grains. In contrast, Ni, Co, and As were not mobilized. External fluid infiltration is negligible and is indicated only by minor, compositionally distinct, late sulfide veinlets crosscutting the conglomerates. Sulfur isotope analysis of detrital pyrite yields generally positive (delta(34)S values (0.97-9.26%0). The delta(34)S sulfur isotope composition of pyrite overgrowths and postdepositional grains overlaps the isotopic range of the detrital grains, suggesting a near-closed S system during postd.epositional processes. However, the detrital pyrite tends to have slightly negative Delta(33)S while the postdepositional and overgrowth pyrite are either neutral or slightly positive. The S isotope composition of the detrital pyrite is compatible with an origin of S as dissolved sulfate in an ocean under a low oxygen atmosphere. The potential source of the Au-bearing detrital pyrite appears to have been an, as yet, undiscovered Archean deposit located within 1 to 8 kin of the placer deposit.

In Situ Trace Element and Sulfur Isotope Analysis of Pyrite in a Paleoproterozoic Gold Placer Deposit, Pardo and Clement Townships, Ontario, Canada

Previous experiments have characterized the behavior of uranium in sulfide-carbonate solutions at 200/sup 0/C, analogous to the solutions that produced many endogenous pitchblende deposits, as indicated by fluid inclusions in minerals and by mineralogical and geochemical data. Molybdenum often accompanies uranium in endogenous pitchblende and related deposits and may form economic accumulations as low-temperature molybdenite. There have been repeated discussions on the forms taken by molybdenum and the reasons for deposition in such ores. The experiments described here indicate the existence of various complexes of molybdenum under different conditions and explain some of the paragenesis of molybdenum minerals with uranium minerals. 12 references, 3 figures, 1 table.

Experimental study of the behavior of molybdenum in hot sulfide-carbonate solutions

The distribution of rhenium in the profile of an ore-controlling zonation in complex exogenic, uranium-coal deposits is described. It is established that the earlier suggested distinct association between rhenium and molybdenum is lacking in the ores. The possibility of rhenium mineralization in the deposit is noted.

Rhenium in infiltration uranium–coal deposits

Allowance for solubility of mineral components when determining absolute age of uranium ores

Uranyl minerals form a distinct series based on their solubilities in environments of different pH, beginning with the molybdenates, and proceeding through the arsenates, phosphates, vanadates, and silicates of the soddyite groups. Unlike exogenetic-epigenetic uranium deposits with pitchblende, infiltrational deposits with uranyl mineralization are primarily the result of changes in the pH of the environment. The model presented gives the precipitation of uranyl vanadates at an acidic geochemical barrier, and it can be used to explain the genesis of carnotite deposits in calcretes. A geochemically opposite model for the formation of uranyl minerals as the result of the neutralization of interstitial waters that have been strongly acidified (to pH 2) in conjunction with the oxidation of sulfide-bearing rocks must be adopted to explain the distribution and conditions of the formation of the uraninite deposits in black shales. (JMT)

Ye. M. Shmariovich

Papers

Experimental study of the behavior of molybdenum in hot sulfide-carbonate solutions

Rhenium in infiltration uranium–coal deposits

Allowance for solubility of mineral components when determining absolute age of uranium ores

Role of pH changes in primary uranite mineralization

Two classes of ores and ore-controlling layered zonation in epigenetic deposits of uranium