ALBERT

Description: The Handan-Xingtai district in the North China craton is one of the most important concentrations of iron skarn deposits in China, with proven reserves of 900 to 1,000 Mt at an average of 40 to 55 wt % Fe. The iron mineralization occurs predominantly along contact zones between Early Cretaceous intermediate-silicic intrusions and Middle Ordovician marine carbonates intercalated with numerous evaporite beds. In this paper, we present textural features and laser ablation ICP-MS U-Pb dating results of hydrothermal zircon from five major iron skarn deposits to place tight constraints on the timing and duration of the district-scale iron mineralization. Zircon grains from the mineralized skarns are anhedral to subhedral crystals and euhedral tetragonal bipyramids. They are closely intergrown or texturally associated with diopside, garnet, epidote, calcite, albite, and phlogopite. Other common minerals in the skarn assemblages include F-rich hornblende, wilkeite-F, F-apatite, and fluorite. Zircon grains typically contain abundant inclusions of skarn minerals and daughter mineral-rich (mostly magnetite, halite, and sylvite) fluid inclusions. Compositionally, these zircon grains have moderately to extremely high Th (518–7,477 ppm) and U (109–25,610 ppm) contents, with highly variable Th/U ratios ranging from 0.01 to 5.23. The morphological, textural, and geochemical features of the zircons confirm their hydrothermal origin and indicate that they most likely precipitated from high-temperature, F-rich, magmatic-derived ore-forming fluids. The hydrothermal zircon grains yield well-defined concordant U-Pb ages for the five studied iron skarn deposits, with weighted mean 206 Pb/ 238 U dates ranging from 133.6 ± 0.9 to 128.5 ± 1.4 Ma (2 ). These ages are remarkably consistent with U-Pb ages (134.1 ± 1.2 to 128.5 ± 0.9 Ma; 2 ) of magmatic zircon grains from the ore-related intrusions in each deposit, demonstrating that iron skarn mineralization was genetically related to the coeval magmatism. Our new geochronological data, when combined with existing isotopic ages, indicate that iron mineralization and associated magmatism in the Handan-Xingtai district took place mainly at the ca. 137–133 and 131–128 Ma intervals. Iron skarn deposits of similar ages also occur widely in other parts of the eastern North China craton, forming the only known giant Mesozoic iron skarn province in a cratonic block on the Earth. The formation of these iron skarn deposits and associated intrusions coincided in time with lithospheric thinning or destruction of the North China craton, strongly suggesting a causal link between the two processes.

Description: The Kangdian iron oxide copper-gold (IOCG) metallogenic province contains a number of economically important Fe-Cu deposits in South China and northern Vietnam. Due to the lack of precise mineralization ages, the metallogenesis of this province has long been a matter of debate. In this study, molybdenite Re-Os, pyrite Re-Os, and Rb-Sr isotope methods are used to date the Yinachang and E’touchang Fe-Cu deposits in the central part of this province. Fine-grained (〈0.1 mm) molybdenite occurs as veinlets along bandings or fractures of magnetite ores and hydrothermal veins in the Yinachang deposit. Molybdenite separates from magnetite ores have highly reproducible Re-Os model ages of 1654 ± 7 Ma, whereas those from hydrothermal veins have a much younger Re-Os model age of 1451 ± 6 Ma. Euhedral pyrite grains occur locally along foliations of hematite ores and their proximal alteration assemblages in the E’touchang deposit. Pyrite separates have an Re-Os isochron age of 1487 ± 110 Ma and a single-grain Rb-Sr isochron age of 1453 ± 28 Ma, both of which are compatible with the molybdenite Re-Os age of hydrothermal veins from the Yinachang deposit. The molybdenite age of magnetite ores is in good agreement with zircon U-Pb ages of dolerite intrusions in the region, and is considered to represent the timing of a major ore formation event at ~1655 Ma. The younger Re-Os and Rb-Sr ages likely record a secondary hydrothermal overprint event at ~1450 Ma, which has not been recognized before. The mineralization potential and implications of this event need to be investigated in future studies. Our new isotopic data set hence demonstrates that the Kangdian IOCG deposits were likely formed at ~1655 Ma, synchronous with the late Paleoproterozoic intracontinental rifting event of the western Yangtze block.

Description: Deletions and gains of chromosomal segments detectable cytogenetically have long been recognized as valuable tools for AML classification and prognostication. Segmental amplifications and deletions can be reliably detected at the whole genome level using array-based CGH. In this study, we utilized a novel dense tiling path array consisting of 386,165 unique isothermal (Tm=76°C) oligomers (average length 51 nt) spaced evenly at ~6Kb intervals across the genome. We analyzed 144 adult de novo AML samples: 64 had normal karyotypes, and 80 had 1 or 2 clonal, balanced or unbalanced abnormalities (samples with ≥3 clonal chromosome aberrations were excluded). Similar numbers of FAB M0/1, M2, M3, and M4 cases were included, and all samples had 〉30% blasts. Bone marrow-derived tumor DNA or control DNA derived from the blood of 23 normal individuals (matched for age and ethnicity, and with no history of cancer) was co-hybridized with a control pool of DNAs derived from the blood of 4 healthy young males. Of the 23 gains and losses detected cytogenetically in 〉20% of metaphases, 22 (96%) were also detected by CGH. Of the 20 copy number changes present in ≤20% of metaphases, CGH detected only 7 (35%). CGH identified X chromosome number correctly in all samples. Further, a number of previously described segmental copy number polymorphisms (CNPs; Sebat et al, Science2004;305:525) were identified in both the AML samples and the normal control population. Using very stringent criteria to define abnormal segments (≥8 consecutive oligomers with log2 values of at least +/− 0.5), we identified 47 independent loci in the AML samples that had abnormal segments that were not apparent cytogenetically (mostly due to small size). Thirteen of these were present in multiple AML samples (range 2–22), but were also present in at least one cancer-free control sample, or were previously identified in normal individuals. These clearcut CNPs tended to be small (