Application of apatite fission-track analysis and zircon U-Pb geochronology to study the hydrothermal ore deposits in the Lesser Hinggan Range: Exhumation history and implications for mineral exploration

This study uses apatite fission track (AFT) and zircon U-Pb data to reveal the cooling history of bedrocks from the Dong'an, Cuihongshan and Pingdingshan deposits in the Lesser Hinggan Range, which is one of the most important metallogenic districts in NE China. AFT results and modeling of samples identified three cooling phases since late Mesozoic times. Stage one recorded rapid cooling to the low temperature part of the fission track partial annealing zone at circa 100 +/- 10 degrees C during ca. 90-70 Ma with an average exhumation rate of similar to 29-58 m/Ma. Stage two was a relatively slow cooling period occurring between similar to 70 and 25 Ma with an average exhumation rate of similar to 12 m/Ma, suggesting that the Lesser Hinggan Range had been denuded to an area of low relief. Stage three was an increased cooling period took place from the Miocene to Quaternary (< 25 Ma) with an average exhumation rate of similar to 47 m/Ma, which transported the sampled rocks to the present surface at an increased exhumation rate. Zircon U-Pb dating of magmatic rocks from the three deposits yielded Concordia ages of 188.8 +/- 0.5 Ma (alkali-feldspar granite) and 115.6 +/- 0.4 Ma (rhyolitic porphyry) at the Dong'an deposit, yielded Concordia ages of 195 +/- 1 Ma (alkali-feldspar granite) and 200.3 +/- 0.5 Ma (monzonitic granite) at the Cuihongshan deposit, and yielded Concordia ages of 259.4 +/- 0.82 Ma (Biotite granit) and 225.9 +/- 1.1 Ma (dioritic dyke) at the Pingdingshan deposit, which are notably older than their corresponding AFT ages. Our results, combined with other data in and/or around NE Asia (Great Hinggan, Changbai Mts, Yanji, Sikhote Alin Mts, South Korea and SW Japan), suggest micro-continental blocks in NE Asia underwent different uplifting/denudation rates since the Late Cretaceous, which indicates that the Xing'an, Songliao and Nadanhada-SikhoteAlin accretionary complex blocks may have good potential for mineral exploration to great depths.