Study On The Genesis Of Typical Deposits In Ma'anshan Turquoise Metallogenic Belt Of Ningwu Basin

Ma'anshan turquoise metallogenic belt is located at the middle section of the Ningwu Basin in the Middle-lower Yangtze River polymetallic metallogenic belt.In this study,two representative turquoise deposits,Dahuangshan and Bijiashan,have been carefully studied.Based on the detailed field geological investigation and indoor experimental analysis,the genesis of the turquoise deposits and ore-forming processes have been carried out,the prospecting sign and ore-prospecting orientation have been summarized,aiming to enrich and improve the metallogenic theory of turquoise deposit.The deposits in the Ma'anshan turquoise ore belt are associated deposits of the porphyrite magnetite deposits in the basin.Apatite-bearing magnetite is the main ore-forming rock of the turquoise deposits and the orebodies are presented in the kaolinization magnetite(rock or vein)and joint fissures of surrounding rock.Turquoise deposits formed through the pseudo-mineralization(turquoise+kaolinite)and hydrothermal mineralization(turquoise+kaolinite+pyrite+quartz)stages.Turquoise ore outputs in the form of pseudo-morphology,nodules and veinsThe turquoise minerals of the Ma'anshan turquoise ore belt show a dense microcrystalline-scaly,irregular spheroidal,and radial fiber spheroidal gelatinous structure.Both ore-forming methods,impurity minerals and recrystallization affected the structure and mineral crystals degree of turquoise.During mineralization and crystallization of the turquoise,Fe3+and Al3+in the crystal structure could be completely replaced by isomorphism.With the increase of TFeO content,the color of turquoise changed from blue to green and yellow-green.When TFeO content was greater than CuO content,turquoise could be classified as aphosphite(iron turquoise)in the turquoise mineral family.The symbiosis pyrites with turquoise show pentagonal dodecahedron and cubic crystal,and have Co/Ni value of 32-51 and ?34S value of 8.3-11.9‰,proving that the ore-forming hydrotherm originated from volcanic exhalation.The ore-forming fluids mainly derived from atmospheric precipitation with a small amount of magmatic water.According to the features of mineral assemblage,the temperature of ore-forming fluid was estimated about 270?,and ore-forming fluid was acid.Both turquoise and apatite mostly contain P2O5 and have similar compositions of trace element and rare earth elements,implying that apatite was the main source for P in the turquoise.The symbiosis pyrites with turquoise point out that Cu was derived from volcanic magma hydrotherm.Altered minerals show that Fe and Al were originated from magnetite and albite in ore-forming parental rock.Comprehensive study has found that turquoise deposits in the Ma'anshan turquoise metallogenic belt from the Ningwu Basin,were the origin of the medium-low temperature ore-forming hydrothermal alteration(filling)formed by the terrestrial volcanism.Ore-forming rocks has undergone low-and medium-temperature hydrothermal alteration and metasomatism,occurring turquoise mineralization.Then,turquoise accumulated and mineralized in tectonic fractures of ore-forming parent rocks and surrounding rock of(pyroxene)dioritic porphyrite Massive kaolinization,phosphate minerals(e.g.blue pyrite and arsenite)on the surface and secondary copper-containing minerals(e.g.malachite)are important signs for ore prospecting.The further prospecting directions are closely related with the porphyrite type iron ore in the continental volcanic formations.