Natural analogues: Alamosa River monzonite intrusive into tuffaceous and andesitic rocks

Conference · Sat Jan 01 04:00:00 EST 1983 · Mater. Res. Soc. Symp. Proc.; (United States)

OSTI ID:5976069

Brookins, D G ^[1]; Abashian, M S; Cohen, L H; Williams, A E; Wollenberg, H A; Flesser, S

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1. Univ. of New Mexico, Albuquerque

This project encompasses investigations of selected natural analogues of minerals and rocks containing radioelements and fission-product elements, to ascertain how radionuclides and their daughter elements may migrate from sites or origin in response to long-term natural processes such as heating due to an igneous intrusion, circulating hydrothermal systems, diffusion through the rock matrix, weathering and erosion. Comparison of natural occurrences with conceptual models based on laboratory data will furnish a test of such models over time periods comparable to or longer than those expected for a repository. For this study, we have examined large-scale intrusions of igneous rocks which have profoundly affected the thermal and hydrologic settings of large masses of surrounding country rock, and occurrences where migration of elements has occurred after intrusion and subsequent cooling. Specifically, we have investigated the Alamosa River stock, intrusive into tuffaceous rocks and andesites of the Platoro Caldera in the San Juan Mountains of southern Colorado. The oxygen isotopic studies show the effect of extensive hydrothermal activity on the intruded rocks, as well as the host tuffaceous and flow rocks. Convective cooling has been demonstrated for the Alamosa River Stock. The distribution of U, Th, REE, V, K, Ti, in each rock is apparently unaffected by the intrusion. This is true also for Rb, Sr, Ta, Na, and others, although for some of these elements there is no strong chemical gradient between the rocks. Some elements show some evidence for contact zone mobility, but only within ten meters or so of the contact (Cs, Cr, Co). Both the mozonite and tuff have retained their bulk chemistry during and after intrusion. The absence of elemental migration between the tuffs and monzonites, even in a convective system, supports continued assessment of such rocks for radwaste repository consideration.

• OSTI ID: 5976069
• Report Number(s): CONF-821107-Pt.1
• Conference Information: Journal Name: Mater. Res. Soc. Symp. Proc.; (United States) Journal Volume: 15
• Country of Publication: United States
• Language: English

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