The Baoshan Block is tectonically located in the middle segment of the Sibumasu plate. Granitic magmatism within the Baoshan Block has been considered weakly active due mainly to very limited exposures during the Hima...The Baoshan Block is tectonically located in the middle segment of the Sibumasu plate. Granitic magmatism within the Baoshan Block has been considered weakly active due mainly to very limited exposures during the Himalaya orogenic episode. The geochronological study on the buried Shuangmaidi granite has confirmed the existence of the Cenozoic granitoids in the Baoshan Block. The present study indicates that： （1） It is medium- to coarse-grained two mica phyric granite, characterized by high SiO2 （73.55%-77.16%） and low CaO （0.34%-1.38%） contents, with a total alkalis （K2O＋Na2O） of 5.22%-8.03%, K2O/Na2O ratios of 0.24-1.79, and total rare earth elements （ZREE） of the granite between 85 and 125 ppb. All samples are enriched in light REE and exhibit medium negative Eu anomalies; and they show pronounced negative anomalies in Ba, Sr, Ti, and Nb but significant positive anomalies in K, Rb, U, Th, and Pb on mantle-normalized trace element patterns, indicating typi-cally peraluminous to strongly peraluminous S-type granite. （2） The zircon SHRIMP U-Pb ages of the granite are 36.27±0.48 Ma for the samples from ZK7-1 and 35.78±0.49 Ma for those from ZK0-1, respectively. The similar zircon ages from these two drill cores may suggest that the granite samples come from the same buried pluton. （3） 206pb/204pb values of the granite vary from 20.115 to 25.359, 207pb/204pb from 15.776 to 16.160, and 208pb/204pb from 39.236 to 41.285, showing the characteristics of radio- active lead anomaly of the upper crust. The （87Sr/86Sr）i values calculated on the average age of the two-mica orthoclase granite （36 Ma） range from 0.72524 to 0.77503 and eNd（t） values vary from -10.9 to -11.7. These data, along with the depleted-mantle Nd modal ages of 1.73-1.80 Ga, imply that the granites might have formed from partial melting of the Precambrian crystal basements. （4） On the Hf-Rb-Ta diagram, almost all the samples fall within the field of post-collision tectonic setting. The CaO/Na2O and A1203/TiO2 ratios suggest that the granitic magma may have formed from partial melting of clay-rich crustal materials with a pos- sible melting temperature of about 900℃ and a possible crystallization temperature of 775-795~C. （5） During the post-collision of the Himalaya orogen, with the southeastward extrusion of the Indochina continent resulting from the continuous northward indentation of the India continent into the Asia, the Gaoligong Fault, as the western boundary of the Indochina continent, moved in the dextral strike-slip on a large scale to trigger partial melting of the thickened crust, and the peraluminous granitic magma from which the Shuangmaidi two-mica orthoclase granite derived was formed.展开更多
Platinum has been one of the highly needed mineral resources in China.The geochemical exploration at two survey scales was applied in telescoping ore targets for the first time in Eastern Yunnan Pt geochemical provinc...Platinum has been one of the highly needed mineral resources in China.The geochemical exploration at two survey scales was applied in telescoping ore targets for the first time in Eastern Yunnan Pt geochemical province that was delineated using Pt data from flood plain sediments with extra-low sampling density.Our study was based on the delineations and assessments of both regional and local Pt anomalies using the Pt data by analyzing with C-OES the composite samples with two sampling densities.The composite samples were obtained by recomposing at two sampling densities the original stream sediment samples collected by the National Geochemical Mapping Project.Semivariograms were used to quantitatively describe the variability of Pt anomalies and further analyze the factors controlling the variability.Pt resource potentials of both the regional Pt anomalies and the local Pt anomalies in the study area were estimated based on the geochemical block methods,respectively.It comes to the conclusions as follows.(1) From the regional to local Pt anomaly,the factors controlling their variability from the deep seated faults-basalts turn into the basalts-branch faults,which suggest that Semivariograms could identify the geological factors controlling the variability of the Pt anomalies identified by the Pt data from the stream sediments with different sampling densities.(2) There exist two types of Pt anomalies in the study area.One is those displaying at sampling densities,and its average Pt concentration significantly increases with sampling density increasing.The other is getting weaker and/or disappears with sampling density increasing.This shows that TOTGEMS could gradu-ally eliminate non-ore anomalies and keep ore anomalies.(3) The average Pt concentration of the local Pt anomaly blocks delineated using Pt data from stream sediments with sampling density of one composite per 16 km2 is twice as much as that of the regional Pt anomaly blocks delineated using Pt data from stream sediments with sampling density of one composite per 64 km2.The Pt resource amount of the local Pt anomaly blocks is 60% of the regional anomaly blocks,but the area of the former is just 35% of the latter,which suggests that the Pt resource amount is mainly concentrated in its local anomalies,and that TOTGEMS has a good exploration function that efficiently approaches ore targets.展开更多
基金supported by National Natural Science Foundation of China (GrantNos. 40772197,40972232)National High-Tech Research & Development (Grant No. 2006BAB01A03)National Support Program of Science & Technology (Grant Nos. 2006BAB01A01,2006BAB01A03)
文摘The Baoshan Block is tectonically located in the middle segment of the Sibumasu plate. Granitic magmatism within the Baoshan Block has been considered weakly active due mainly to very limited exposures during the Himalaya orogenic episode. The geochronological study on the buried Shuangmaidi granite has confirmed the existence of the Cenozoic granitoids in the Baoshan Block. The present study indicates that： （1） It is medium- to coarse-grained two mica phyric granite, characterized by high SiO2 （73.55%-77.16%） and low CaO （0.34%-1.38%） contents, with a total alkalis （K2O＋Na2O） of 5.22%-8.03%, K2O/Na2O ratios of 0.24-1.79, and total rare earth elements （ZREE） of the granite between 85 and 125 ppb. All samples are enriched in light REE and exhibit medium negative Eu anomalies; and they show pronounced negative anomalies in Ba, Sr, Ti, and Nb but significant positive anomalies in K, Rb, U, Th, and Pb on mantle-normalized trace element patterns, indicating typi-cally peraluminous to strongly peraluminous S-type granite. （2） The zircon SHRIMP U-Pb ages of the granite are 36.27±0.48 Ma for the samples from ZK7-1 and 35.78±0.49 Ma for those from ZK0-1, respectively. The similar zircon ages from these two drill cores may suggest that the granite samples come from the same buried pluton. （3） 206pb/204pb values of the granite vary from 20.115 to 25.359, 207pb/204pb from 15.776 to 16.160, and 208pb/204pb from 39.236 to 41.285, showing the characteristics of radio- active lead anomaly of the upper crust. The （87Sr/86Sr）i values calculated on the average age of the two-mica orthoclase granite （36 Ma） range from 0.72524 to 0.77503 and eNd（t） values vary from -10.9 to -11.7. These data, along with the depleted-mantle Nd modal ages of 1.73-1.80 Ga, imply that the granites might have formed from partial melting of the Precambrian crystal basements. （4） On the Hf-Rb-Ta diagram, almost all the samples fall within the field of post-collision tectonic setting. The CaO/Na2O and A1203/TiO2 ratios suggest that the granitic magma may have formed from partial melting of clay-rich crustal materials with a pos- sible melting temperature of about 900℃ and a possible crystallization temperature of 775-795~C. （5） During the post-collision of the Himalaya orogen, with the southeastward extrusion of the Indochina continent resulting from the continuous northward indentation of the India continent into the Asia, the Gaoligong Fault, as the western boundary of the Indochina continent, moved in the dextral strike-slip on a large scale to trigger partial melting of the thickened crust, and the peraluminous granitic magma from which the Shuangmaidi two-mica orthoclase granite derived was formed.
基金Supported by National High-Tech Research & Development Program of China (863 Program) (Grant No. 2006AA06Z113)National Natural Science Foundation of China (Grant No. 40772197)
文摘Platinum has been one of the highly needed mineral resources in China.The geochemical exploration at two survey scales was applied in telescoping ore targets for the first time in Eastern Yunnan Pt geochemical province that was delineated using Pt data from flood plain sediments with extra-low sampling density.Our study was based on the delineations and assessments of both regional and local Pt anomalies using the Pt data by analyzing with C-OES the composite samples with two sampling densities.The composite samples were obtained by recomposing at two sampling densities the original stream sediment samples collected by the National Geochemical Mapping Project.Semivariograms were used to quantitatively describe the variability of Pt anomalies and further analyze the factors controlling the variability.Pt resource potentials of both the regional Pt anomalies and the local Pt anomalies in the study area were estimated based on the geochemical block methods,respectively.It comes to the conclusions as follows.(1) From the regional to local Pt anomaly,the factors controlling their variability from the deep seated faults-basalts turn into the basalts-branch faults,which suggest that Semivariograms could identify the geological factors controlling the variability of the Pt anomalies identified by the Pt data from the stream sediments with different sampling densities.(2) There exist two types of Pt anomalies in the study area.One is those displaying at sampling densities,and its average Pt concentration significantly increases with sampling density increasing.The other is getting weaker and/or disappears with sampling density increasing.This shows that TOTGEMS could gradu-ally eliminate non-ore anomalies and keep ore anomalies.(3) The average Pt concentration of the local Pt anomaly blocks delineated using Pt data from stream sediments with sampling density of one composite per 16 km2 is twice as much as that of the regional Pt anomaly blocks delineated using Pt data from stream sediments with sampling density of one composite per 64 km2.The Pt resource amount of the local Pt anomaly blocks is 60% of the regional anomaly blocks,but the area of the former is just 35% of the latter,which suggests that the Pt resource amount is mainly concentrated in its local anomalies,and that TOTGEMS has a good exploration function that efficiently approaches ore targets.
