Abstract
The Jinchangyu Au deposits contained an original resource of 50 t of gold and is located close to the northeastern
margin of the North China Craton (NCC). The orebodies are controlled by structures in the amphibolite units of
the Archaean Zunhua Group. Mineralization is generally associated with albite and hematite which is indicative
of Na–Al–Si–Fe alteration. The most common styles of mineralization are subdivided based on the cross-cutting
relationships of mineral assemblages as follows: (i) quartz–albite–hematite; (ii) quartz–albite–polymetallic
sulfides with gold and molybdenite; (iii) quartz–pyrite; and (iv) quartz–carbonate. Quartz samples from the second (Stage II) and third (Stage III) assemblages contain two-phase fluid inclusion types; these are: (i) CO2–H2O
fluid inclusions, and (ii) daughter mineral-bearing inclusions, which have homogenization temperatures of
270°–350 °C (for assemblage Stage II) and 180°–240 °C (for Stage III), and salinities of ≤13 wt.% NaCl equiv. A
few S-type fluid inclusions suggesting salinities of 27.6–28.3 wt.% NaCl equiv. The S isotope composition of pyrite
and molybdenite from Stage II (δ34S = –4.4 to 1.9‰) indicates that the mineralizing fluid originated predominantly from a magmatic source. The H–O isotope signatures from Stage II indicate a magmatic-dominated source
for the mineralizing fluid with some addition of meteoric fluids. Previously published Pb and C isotope data
indicate that ore and magma in the eastern part of the Hebei Province of China interacted with Precambrian
country rocks, and so the fluids moved from the lower crust to shallower level during mineralization. The red
quartz–albite–hematite veins from Jinchangyu were generated under strongly oxidizing alkaline conditions
that were favorable for the incorporation of gold into the fluid and the crystallization of albite during the early
stage of gold deposition.
Seven molybdenite samples from Jinchangyu yield Re–Os model ages of ca. 233 to 219 Ma with a weighted
mean age of 225 ± 4 Ma and an isochron age of 223 ± 5 Ma. This indicates that at least some of the gold
associated with molybdenite is Late Triassic in age, and could be associated with buried intrusions that
are part of the Late Triassic Dushan granites in the eastern portion of the NCC. This mineralization was
formed after the closure of the Paleo-Asian Ocean. These results indicate that the intrusion-related Jinchangyu
deposit is the far-field structural product of the collision of the NCC with the Siberian Craton to the north
along the northern margin of the NCC
margin of the North China Craton (NCC). The orebodies are controlled by structures in the amphibolite units of
the Archaean Zunhua Group. Mineralization is generally associated with albite and hematite which is indicative
of Na–Al–Si–Fe alteration. The most common styles of mineralization are subdivided based on the cross-cutting
relationships of mineral assemblages as follows: (i) quartz–albite–hematite; (ii) quartz–albite–polymetallic
sulfides with gold and molybdenite; (iii) quartz–pyrite; and (iv) quartz–carbonate. Quartz samples from the second (Stage II) and third (Stage III) assemblages contain two-phase fluid inclusion types; these are: (i) CO2–H2O
fluid inclusions, and (ii) daughter mineral-bearing inclusions, which have homogenization temperatures of
270°–350 °C (for assemblage Stage II) and 180°–240 °C (for Stage III), and salinities of ≤13 wt.% NaCl equiv. A
few S-type fluid inclusions suggesting salinities of 27.6–28.3 wt.% NaCl equiv. The S isotope composition of pyrite
and molybdenite from Stage II (δ34S = –4.4 to 1.9‰) indicates that the mineralizing fluid originated predominantly from a magmatic source. The H–O isotope signatures from Stage II indicate a magmatic-dominated source
for the mineralizing fluid with some addition of meteoric fluids. Previously published Pb and C isotope data
indicate that ore and magma in the eastern part of the Hebei Province of China interacted with Precambrian
country rocks, and so the fluids moved from the lower crust to shallower level during mineralization. The red
quartz–albite–hematite veins from Jinchangyu were generated under strongly oxidizing alkaline conditions
that were favorable for the incorporation of gold into the fluid and the crystallization of albite during the early
stage of gold deposition.
Seven molybdenite samples from Jinchangyu yield Re–Os model ages of ca. 233 to 219 Ma with a weighted
mean age of 225 ± 4 Ma and an isochron age of 223 ± 5 Ma. This indicates that at least some of the gold
associated with molybdenite is Late Triassic in age, and could be associated with buried intrusions that
are part of the Late Triassic Dushan granites in the eastern portion of the NCC. This mineralization was
formed after the closure of the Paleo-Asian Ocean. These results indicate that the intrusion-related Jinchangyu
deposit is the far-field structural product of the collision of the NCC with the Siberian Craton to the north
along the northern margin of the NCC
Original language | English |
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Pages (from-to) | 313-329 |
Number of pages | 17 |
Journal | Ore Geology Reviews |
Volume | 73 |
Early online date | 20 Nov 2014 |
Publication status | Published - Mar 2016 |