Carbon isotope geochemistry of graphite deposits and ore-bearing khondalite series in North China: implications for several geoscientific problems.

A database of 102 analyses of delta(13)C(PDB) for graphite deposits and ore -bearing khondalite series in North China clearly shows several regularitie s: 1) delta(13)C(gneiss graphite)<<delta(13)C(diopsidite) (graphite)<delta( 13)C(marble) (graphite)<delta(13)C(graphite-marble) (calcite)<delta(13)C(ma rble) (calcite;) 2) the values of delta(13)C(migmatite graphite) are always between those of organic carbon and inorganic carbon; 3) the averages of d elta(13)C(gneiss graphite) for different terrains, ranging from -22. 8 part s per thousand to -21. 48 parts per thousand, are consistent completely, an d slightly lower than the average of -26+/-7 parts per thousand for organic matter from the world; 4) delta(13)C for the protolith of marble is estima ted over 2 parts per thousand, which is consistent with the worldwide delta (13)C(carb) positive excursion in the period of 2330 similar to 2060 Ma. Co nclusions are drawn out as below: (1) geofluid is an important constraint o n fractionation and homogenization of carbon isotopes, one of three carbon sources for graphite mineralization, one of five existing forms of carbon, and a key media and style of carbon circulation as wen; (2) it is unbelieva ble that, only stemmed from delta(13)C(calcite)congruent to-5 parts per tho usand, ore-forming fluid and material for hydrothermal deposits are derived from mantle, because many factors can cause hydrothermal delta(13)C(calcit e) equal to about - 5 parts per thousand; (3) the khondalite series in Nort h China are mainly developed in Paleoproterozoic, most likely, in the perio d of 2300 similar to 2050 Ma.