TY - JOUR
T1 - Fluid and mineral inclusions in cloudy diamonds from Koffiefontein, South Africa
AU - Izraeli, Elad S.
AU - Harris, Jeffrey W.
AU - Navon, Oded
PY - 2004/6/1
Y1 - 2004/6/1
N2 - Silicates, carbonates and brine were detected in microinclusions in cloudy diamonds from Koffiefontein. The silicates belong to either the eclogitic or the peridotitic paragenesis. They are similar in composition to the larger mineral inclusions found in other Koffiefontein diamonds and record similar pressures and temperatures of formation (1000-1200°C, 4-6 GPa). The clouds also carry additional mineral phases that were not detected before in Koffiefontein: phlogopite, high-Si mica, an Al-Mg-rich phase and carbonates. In many cases silicate minerals coexist together with brine in individual microinclusions. Brines associated with either eclogitic or peridotitic minerals have similar composition and both are rich in water, Cl, K and carbonates (Izraeli et al., 2001). The above findings, together with the high proportion of cloudy diamonds in Koffiefontein, suggest that brine penetration into neighboring peridotitic and eclogitic rocks was pervasive. The high carbon content of the brine (as dissolved carbonates) initiated diamond growth in both rock types, most, on preexisting diamonds that now form inclusion-free cores. The low aggregation state of nitrogen in the cloudy diamonds, relative to other diamonds from Koffiefontein indicates either a somewhat lower temperature of storage in the mantle (which may be the reason for the presence of brine rather than melt) or a young event of cloudy diamond formation.
AB - Silicates, carbonates and brine were detected in microinclusions in cloudy diamonds from Koffiefontein. The silicates belong to either the eclogitic or the peridotitic paragenesis. They are similar in composition to the larger mineral inclusions found in other Koffiefontein diamonds and record similar pressures and temperatures of formation (1000-1200°C, 4-6 GPa). The clouds also carry additional mineral phases that were not detected before in Koffiefontein: phlogopite, high-Si mica, an Al-Mg-rich phase and carbonates. In many cases silicate minerals coexist together with brine in individual microinclusions. Brines associated with either eclogitic or peridotitic minerals have similar composition and both are rich in water, Cl, K and carbonates (Izraeli et al., 2001). The above findings, together with the high proportion of cloudy diamonds in Koffiefontein, suggest that brine penetration into neighboring peridotitic and eclogitic rocks was pervasive. The high carbon content of the brine (as dissolved carbonates) initiated diamond growth in both rock types, most, on preexisting diamonds that now form inclusion-free cores. The low aggregation state of nitrogen in the cloudy diamonds, relative to other diamonds from Koffiefontein indicates either a somewhat lower temperature of storage in the mantle (which may be the reason for the presence of brine rather than melt) or a young event of cloudy diamond formation.
UR - http://www.scopus.com/inward/record.url?scp=2442622351&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2003.09.005
DO - 10.1016/j.gca.2003.09.005
M3 - Article
AN - SCOPUS:2442622351
VL - 68
SP - 2561
EP - 2575
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
SN - 0016-7037
IS - 11
ER -