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The Mofanggou Au deposit is stratoid in form and occurs in an early-Cambrian Zhushadong formation that overlies the principal detachment slip zone between the Cambrian strata and Archaean gneissose granodiorites or Palaeoproterozoic adamellites. Wall-rock alteration includes kaolinisation, pyritisation, silicification, sericitisation, calcitisation and fluoritisation. Au ores are related to pyritisation, silicification and calcitisation. The Au minerals consist of native Au, petzite and electrum. The homogenisation temperatures of the fluid inclusions were in the range 103-220 degrees C and the salinity varied from 4.65% to 13.18 %. S isotope studies showed that the S was derived from the mantle and O isotope analyses revealed that the fluid in the deposit was from mixed magmatic- and atmospheric-water sources., The Mofanggou Au deposit is stratoid in form and occurs in an early-Cambrian Zhushadong formation that overlies the principal detachment slip zone between the Cambrian strata and Archaean gneissose granodiorites or Palaeoproterozoic adamellites. Wall-rock alteration includes kaolinisation, pyritisation, silicification, sericitisation, calcitisation and fluoritisation. Au ores are related to pyritisation, silicification and calcitisation. The Au minerals consist of native Au, petzite and electrum. The homogenisation temperatures of the fluid inclusions were in the range 103-220 degrees C and the salinity varied from 4.65% to 13.18 %. S isotope studies showed that the S was derived from the mantle and O isotope analyses revealed that the fluid in the deposit was from mixed magmatic- and atmospheric-water sources.

The He and Ar isotope characteristics of pyrite from 11 gold deposits and some country rocks were studied. It was found that 3He/4He ratios in gneisses and granites at the edge of the district reflected significant differences in their sources from those of the gold deposits. It is concluded that the mineralising fluids came from deep within the Earth and that multi-stage evolution of a mantle plume resulted in their upward movement to shallower levels, leading to mixing with crustal fluids so that the isotopic characteristics were intermediate between those of mantle and crust., The He and Ar isotope characteristics of pyrite from 11 gold deposits and some country rocks were studied. It was found that 3He/4He ratios in gneisses and granites at the edge of the district reflected significant differences in their sources from those of the gold deposits. It is concluded that the mineralising fluids came from deep within the Earth and that multi-stage evolution of a mantle plume resulted in their upward movement to shallower levels, leading to mixing with crustal fluids so that the isotopic characteristics were intermediate between those of mantle and crust.

The regional geology and gold deposits of the area are discussed from a mantle-plume perspective. The Luxi area was a typical mantle-branch structure in the Mesozoic, comprising an igneous-metamorphic complex, surrounding detachment-slip layers and an overlapping faulted volcanic basin with extensive K-rich volcanic rocks and lamprophyres. Radial and ring faults resulted from uplift of the structure. Gold deposits are related to ductile shear zones and detachment-slip layers, the latter type being more important., The regional geology and gold deposits of the area are discussed from a mantle-plume perspective. The Luxi area was a typical mantle-branch structure in the Mesozoic, comprising an igneous-metamorphic complex, surrounding detachment-slip layers and an overlapping faulted volcanic basin with extensive K-rich volcanic rocks and lamprophyres. Radial and ring faults resulted from uplift of the structure. Gold deposits are related to ductile shear zones and detachment-slip layers, the latter type being more important.

S, Pb, H, O and C isotope data from 13 orefields in eastern Hebei are discussed and various models of metallogenesis considered. It is concluded that gold in the deposits came from the mantle and that ore genesis involved the focusing of mineralising fluids in favourable locations. Prospecting should therefore be concentrated on identifying fluid channels and structures favouring ore deposition., S, Pb, H, O and C isotope data from 13 orefields in eastern Hebei are discussed and various models of metallogenesis considered. It is concluded that gold in the deposits came from the mantle and that ore genesis involved the focusing of mineralising fluids in favourable locations. Prospecting should therefore be concentrated on identifying fluid channels and structures favouring ore deposition.

The source of ore-forming materials for the multi-stage Yanshanian Au, Ag, Cu-Mo, Pb-Zn and Fe deposits of northern Hebei has long been disputed. A large statistical body of isotope data indicates that the materials came from the deep interior of the Earth and migrated episodically in plumes to the surface, where it was emplaced in favourable structures. Of 559 S isotope analyses from 40 ore deposits, most are within the range -5 per mil to +5 per mil with a high degree of homogenisation, indicating that the sulphur was derived mainly from magma. Pb isotope data for 200 samples from 37 deposits indicate that the ore-forming materials were principally of mantle origin; 96 O, H and C isotope analyses from 34 deposits illustrate that the ore-forming fluids were dominated by magmatic water although other sources of water were also involved. It is therefore clear that the formation of the endogenetic deposits was unrelated to the host strata., The source of ore-forming materials for the multi-stage Yanshanian Au, Ag, Cu-Mo, Pb-Zn and Fe deposits of northern Hebei has long been disputed. A large statistical body of isotope data indicates that the materials came from the deep interior of the Earth and migrated episodically in plumes to the surface, where it was emplaced in favourable structures. Of 559 S isotope analyses from 40 ore deposits, most are within the range -5 per mil to +5 per mil with a high degree of homogenisation, indicating that the sulphur was derived mainly from magma. Pb isotope data for 200 samples from 37 deposits indicate that the ore-forming materials were principally of mantle origin; 96 O, H and C isotope analyses from 34 deposits illustrate that the ore-forming fluids were dominated by magmatic water although other sources of water were also involved. It is therefore clear that the formation of the endogenetic deposits was unrelated to the host strata.

The intrusive and orogenic activity that led to emplacement of the deposits is discussed. It is concluded that ore-bearing fluids migrated up and were aggregated along expansion belts during the main metallogenic stage, forming a series of structurally altered and vein-type deposits. These results have been confirmed by deep drilling in the Xinfangzi goldfield. Broadening and enrichment at the top of the orebody resulted from collapse and leaching during upward migration. In light of the findings, special attention should be paid to searching for deep orebodies., The intrusive and orogenic activity that led to emplacement of the deposits is discussed. It is concluded that ore-bearing fluids migrated up and were aggregated along expansion belts during the main metallogenic stage, forming a series of structurally altered and vein-type deposits. These results have been confirmed by deep drilling in the Xinfangzi goldfield. Broadening and enrichment at the top of the orebody resulted from collapse and leaching during upward migration. In light of the findings, special attention should be paid to searching for deep orebodies.

Yuerya is a typical deposit in the hanging wall of the main detachment belt around the East Hebei branch of a mantle plume. It is controlled by antithetic listric faults and subsidiary detachment belts. Yanshanian granite bodies in the area were controlled by complex structures and are characterised by a tower-like distribution; the successive activity of the subsidiary detachment belts resulted in a postdiagenetic granite sill forming a series of low-angle fractures, which became the main expanding structures and ore-forming belt during the major period of mineralisation. The regional ore-forming structures and detailed metallogenic mechanism are discussed. It is thought that there are good prospects for ore at depth., Yuerya is a typical deposit in the hanging wall of the main detachment belt around the East Hebei branch of a mantle plume. It is controlled by antithetic listric faults and subsidiary detachment belts. Yanshanian granite bodies in the area were controlled by complex structures and are characterised by a tower-like distribution; the successive activity of the subsidiary detachment belts resulted in a postdiagenetic granite sill forming a series of low-angle fractures, which became the main expanding structures and ore-forming belt during the major period of mineralisation. The regional ore-forming structures and detailed metallogenic mechanism are discussed. It is thought that there are good prospects for ore at depth.

A study of gold deposits in the area shows that mineralisation was mainly controlled by sources and migration passages of metallogenic materials as well as a favourable structural expansion zone. As well as being partly extracted from ore-bearing country rocks, gold mainly came from depth. Gold-bearing fluids migrated up with the mantle plume, forming various types of deposit such as porphyritic veins, explosion-breccias, large veins and net-shaped veins. The fluids were partly mixed with crust-derived fluids and meteoric water during the upwelling process. Structural deformation was therefore the main ore-controlling factor. The Fuping mantle branch structure linked up with deep-derived ore-forming materials and also constituted a favourable regional tectonic framework. Second-, third- and fourth-order ore-controlling structures were detachments from the mantle branch, the Konnggezhuang fault and second detachment belts along with fault and fissure zones., A study of gold deposits in the area shows that mineralisation was mainly controlled by sources and migration passages of metallogenic materials as well as a favourable structural expansion zone. As well as being partly extracted from ore-bearing country rocks, gold mainly came from depth. Gold-bearing fluids migrated up with the mantle plume, forming various types of deposit such as porphyritic veins, explosion-breccias, large veins and net-shaped veins. The fluids were partly mixed with crust-derived fluids and meteoric water during the upwelling process. Structural deformation was therefore the main ore-controlling factor. The Fuping mantle branch structure linked up with deep-derived ore-forming materials and also constituted a favourable regional tectonic framework. Second-, third- and fourth-order ore-controlling structures were detachments from the mantle branch, the Konnggezhuang fault and second detachment belts along with fault and fissure zones.

A mantle plume dome structure about 200 km in diameter is present in the area. It is surrounded by various strata and structures and has intruded into two different tectonic units. From its centre to the edges it is characterised by: Mesozoic fractures from ductile shear zone to brittle-ductile shear nappe structure and to ductile-brittle fracture zone; Mesozoic ultrametamorphism; Mesozoic magma activities from mantle source magma; and Mesozoic deposits of gold and Ag-polymetallic deposits associated with the semicircular ductile-brittle shear nappe structures. Mineralisation may be the ultimate evolution product of massively upwelling mantle materials and crust-mantle interaction, with the dome structure being the transferral system for ore materials., A mantle plume dome structure about 200 km in diameter is present in the area. It is surrounded by various strata and structures and has intruded into two different tectonic units. From its centre to the edges it is characterised by: Mesozoic fractures from ductile shear zone to brittle-ductile shear nappe structure and to ductile-brittle fracture zone; Mesozoic ultrametamorphism; Mesozoic magma activities from mantle source magma; and Mesozoic deposits of gold and Ag-polymetallic deposits associated with the semicircular ductile-brittle shear nappe structures. Mineralisation may be the ultimate evolution product of massively upwelling mantle materials and crust-mantle interaction, with the dome structure being the transferral system for ore materials.

A study of gold-silver polymetallic mineralisation in northern Hebei reveals that tectonic activity was the leading factor controlling the ore-forming process. Besides being partly derived from ore-bearing wall rocks, gold, silver and some other elements came mainly from depth. Multistage evolution of a mantle plume resulted in the formation of deep channelways for migration of ore materials. The ductile shear zone along the Yanshanian axial part of the orogenic belt caused depressurisation and unloading of the deeper part, which resulted in the ascent of anatectic magma and the formation of third-order-mantle branching of the mantle plume. This was controlled by ductile shear zones. Folding and erosion exposed basement rocks at the surface leading to the formation of a typical metamorphic core complex. The mantle-branching structure not only served as an important system for releasing thermal energy but also controlled the migration and concentration of ore-bearing fluids. Three major tectonomagmatic metallogenic series have been recognised, which are respectively related to mantle thermal fluid activity, ductile shear zones and tectonomagmatic zones., A study of gold-silver polymetallic mineralisation in northern Hebei reveals that tectonic activity was the leading factor controlling the ore-forming process. Besides being partly derived from ore-bearing wall rocks, gold, silver and some other elements came mainly from depth. Multistage evolution of a mantle plume resulted in the formation of deep channelways for migration of ore materials. The ductile shear zone along the Yanshanian axial part of the orogenic belt caused depressurisation and unloading of the deeper part, which resulted in the ascent of anatectic magma and the formation of third-order-mantle branching of the mantle plume. This was controlled by ductile shear zones. Folding and erosion exposed basement rocks at the surface leading to the formation of a typical metamorphic core complex. The mantle-branching structure not only served as an important system for releasing thermal energy but also controlled the migration and concentration of ore-bearing fluids. Three major tectonomagmatic metallogenic series have been recognised, which are respectively related to mantle thermal fluid activity, ductile shear zones and tectonomagmatic zones.