Abstract:

The Yuchiling porphyry-type Mo deposit is located at the northwestern part of the Heyu granitic batholith along the
southern margin of the North China Craton. Zircon LA-ICP-MS U-Pb dating yields an age of 135.2±2.4 Ma for the ore-bearing
parent rock (granite porphyry), and of 138.2±2.3 Ma for the country rock (the unit. 3 intrusion of the Heyu granitic batholith),
indicating that they were all the products of the mid-Early Cretaceous magmatism, and the formation of the Yuchiling Mo deposit should not be older than~135 Ma. The zircon Hf isotope compositions of the Yuchiling ore-bearing granitic porphyry and the
granite country rocks vary greatly. The 176Hf/177Hf values of the former are from 0.281364 to 0.282420 with the εHf(t ) values ranging
from -9.6 to -46.9, and those of the latter are from 0.281774 to 0.282337 with the εHf(t ) values ranging from -12.5 to -32.8,
suggesting that these rocks have undergone a significant magmatic mixing during the crystallization. Also, the mature end-member
is likely to be the Neoarchean-Paleoproterozoic Taihua Group basement and the immature end-member should be the Yanshanian
upwelling and underplating mantle-derived materials or the lower crust reworking of the preexisting mantle-derived constitutes. The
Yuchiling porphyry-type Mo deposit was formed when the Paleo-Pacific regime superposed, destroyed, and transformed the Paleo-
Tethys tectonic systems comprehensively. The intense thinning of the crust induced the underplating or intraplating of the basaltic
magma, leading to partial melting of ancient crustal rocks with higher Mo background, contaminating a small amount of mantlederived
constitutes or juvenile crust materials on different degrees. This Mo-rich magmatic system had experienced a high degree
of differentiation and subsequently ascended to the shallow level of crust and emplaced as granitic porphyry. As the country rock is
granite, the crannies of the porphyry exocontact are few. And for this reason molybdenum mineralization of the ore-bearing porphyry
body have taken place in varying degrees and shown a characteristic of whole-rock mineralization.

Key words: metallogenic age, material source, Mo deposit, Yuchiling, Songxian, Henan Province