Occurrence, chemistry, and origin of immiscible silicate glasses in a tholeiitic basalt: A TEM/AEM study

The occurrence and chemistry of immiscible silicate glasses in a tholeiite mesostasis from the Umtanum formation, Washington, were investigated with transmission electron microscopy and analytical electron microscopy (TEM/AEM). TEM observation reveals isolated, dark globules (2.1 micron or less in diameter) randomly distributed in a transparent matrix glass interstitial to plagioclase laths. The globules less than 0.3 micron and larger than 0.8 micron fall beyond the linear relationship defined by the 0.3–0.8 micron globules in a plot of the logarithm of number versus size. Large globules (0.7 micron or larger in diameter) range from homogeneous to heterogeneous in optical properties and chemistry. Homogeneous globules are completely glassy, whereas heterogeneous globules contain crystalline domains. AEM analyses show that the globules have high Si, Fe, Ca, and Ti with subordinate Mg, Al, P, S, Cl, K, and Mn, which gives high normative fa , px, il , and ap . The matrix glass consists dominantly of Si with low Al and minor Na and K, yielding a high normative qz, or, ab , and an .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47343/1/410_2004_Article_BF00371230.pd

Geology, geochemistry, and some genetic discussion of the Chador-Malu iron oxide-apatite deposit, Bafq District, Central Iran

© 2015, Saudi Society for Geosciences.The Chador-Malu iron oxide-apatite system (Bafq District, Central Iran) contains the largest known iron ore deposit in Iran (pre-mining reserve of 400 Mt @ 55 % Fe), and comprises the pipe-like northern (this study) and the sill-like southern orebodies of predominantly massive ore, and a sodic-calcic alteration envelope. The geology and geochemistry of the Chador-Malu deposit demonstrates its similar characteristics to the Kiruna-type deposits. There is circumstantial evidence for rare earth elements (REE) mobilization during apatite leaching by high-temperature fluids and associated monazite nucleation. Pervasive actinolitization of the rhyolitic country rocks led to the formation of actinolite-rich metasomatic host rocks, which represent another evidence for high-temperature fluids at Chador-Malu. Hydrothermal mineralization is suggested by small iron ore veins (2–3 cm thick) and breccias cemented by iron oxides, as well as a Fe-metasomatism which overprints all types of host rock alteration. Based on REE geochemistry and spatial relationships, it is proposed that a potential source for metals and P could be late-stage Fe-P melt differentiates of the Cambrian magmatism, which is consistent with the late Fe-metasomatism of the host rocks. The proposed Fe-P melts and the mineralization would be linked by hydrothermal media through the zones of ring fracture at Chador-Malu and similar parts of the Bafq district