HR: 16:50h
AN: OS54A-03 [Abstracts]
TI: Autigenic and Anthropogenic Uranium in the Marine Sediments of the Gulf of California in Front of Santa Rosalia Mining District
AU: * Choumiline, K
EM: constan_ayanami@hotmail.com
AF: Universidad Autónoma de Baja California Sur, Carretera al sur s/n. Col. El Calandrio,
La Paz, BCS 23090, Mexico
AU: Rodríguez-Figueroa, G
EM: grodriguezf@hotmail.com
AF: Centro Interdisciplinario de Ciencias Marinas - Instituto Politecnico Nacional, Avenida de
IPN s/n, Col. Playa Palo de Santa Rita, La Paz, BCS 23096, Mexico
AU: Shumilin, E
EM: eshumili@ipn.mx
AF: Centro Interdisciplinario de Ciencias Marinas - Instituto Politecnico Nacional, Avenida de
IPN s/n, Col. Playa Palo de Santa Rita, La Paz, BCS 23096, Mexico
AU: Sapozhnikov, D
EM: sapozz@yandex.ru
AF: V.I.Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academy of
Sciences, Kosygin Str #19, Moscow, BCS 117975, Russian Federation
AB:
To verify the possibilities of U enrichments in the marine sedimentary environment of the eastern sector of the
central Gulf of Califoria (GC), eleven sediment cores were collected in front of the Santa Rosalia mining region,
peninsula of Baja California. Uranium and some other trace element contents in sliced core layers, dried and
homogenized, were determined using instrumental neutron activation analysis. Average total U contents in
sediments of five cores collected in the open GC in front of Santa Rosalía at sites with water depths from 265 m
to 1030 m and in the Guaymas Basin with 2019 m, ranged from 1.36±0.26 mg kg-1 (Guaymas Basin)
to 9.31±3.03 mg kg-1 (SR63 core, depth 630 m). To distinguish non-lithogenic U from the lithogenic
one, the normalization of total U contents to the concentrations of Sc in the samples was used. That because this
element is a reliable indicator of crustal materials, mainly aluminosilicates in the marine sediments. The relative
contribution of non-lithogenic (authigenic) U varied from 49.8±3 % (Guaymas Basin) to 84.2±8.2 %
(SR62 core) of the total U content in the sediments of the open central GC. Surprisingly, in three sediment cores
from the coastal zone adjacent to the town of Santa Rosalía in water depth range 3-6 m very high concentrations
of total U were found, ranging from 54.2±7.3 mg kg-1 (SR4 core) to 110±13 mg kg-1 (SR2
core) and exceeding not only U average abundance in the earth´s crust (2.7 mg kg-1), but also its levels
found for SR62 core, as well as those reported for natural enrichments of U in suboxic-anoxic environments, e.g.
at Mexico and Peru margin sites (3.04 mg kg-1 - 24.54 mg kg-1, McManus et al., 2006). The relative
contribution of non-lithogenic U in the sediments of these three anomalous cores varied from 97.2±0.4 %
(SR4 core) to 98.80.2 % (SR1 and SR2 cores) of their total U content. The sediments were also depleted in
organic C (0.05 % - 0.18 %), which is not typical for marine solid phases enriched in authigenic U. Additional
surface sampling around the cores with high levels of U, helped to define the spatial distribution of this element,
as well as Co, Cu, Zn, light lanthanides and europium, which also showed "anomalies". The association with
anthropogenic impact is discussed because the geochemical fingerprints of these sediments are the same as
for solid wastes of copper smelting, which has occurred in Santa Rosalía in the past century till 1984.
DE: 1065 Major and trace element geochemistry
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 3022 Marine sediments: processes and transport
DE: 4251 Marine pollution (0345, 0478)
DE: 4875 Trace elements (0489)
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly