Geobotanic Remote Sensing for
Mo deposit exploration in dinhu Mo ore-field, Guangdong, China
Xu Huocheng, Xu Resong, Lu
Huiping, Wu Jin Institute of New Technology in Geology, ChineseAcademy of Sciences Xie Yongquan Zhongshan University Abstract As is known, excess Mo in soil would lead to the physiology and ecology variance of plants and their spectrum characteristics change. The authors have studies these variances and carried out a computer manipulation and information collection for the remote sensing information of aerial color infrared, MSS and TM data. The remote sensing data, combined with the spectrum data of plants, are summarized and indicating that it is feasible for using the gobotanary remote sensing to explore hidden deposit into area covered by plants. Geological Setting The investigated area is large scalre porphyry Mo deposit, locating at the Tropic of Cancer. It adjaces to the Dinhu Nature Protectorate UNESCO. It occurs at the Huidong-Goyao E-W extent fault and Sihuo-wuchuan NE extent fault. The strata Middle-lower Devonian series siltstone shale and the magmatic rock is plagiclass grano-phorphyry (gp52(3)), which is a SW-NE extend ellipse rock body. The Mo ore-body occurs at the inside and outside contact of the porphyry body. The alteration zones of the country rock from inside to outside are biotite-k-feldparzation (Bi-Or). Quarts-serisitization, where the Mo mineralization took place quarts-pyritizatiion (Q-Py) and chlorite-phyritizatiion (chl-Py) zone. The distribution of Mo content in rock, soil and plants from Mo ore-body and consistent with that in background area. The correlation coefficients between their Mo contents are more than 0.90 (see table 1). Effect of mo on plant physiology and ecology The effect of Mo on plant physiology and ecology, especially for leguminous plant is investigated. The former researchers consider that Mo can help plant grow. But our results indicate that different Mo content has different effect on plant physiology and ecology. When Mo content in soil is more than 50ppm, it would poison the plants. The higher Mo content is the more serious the poison degree of plants is. For example in the centre of the ore-body, Mo>1200ppm in the soil, the leguminous plants extincted. The leaves of the chief plants such as Itea chnensis, Rhodomyrtus, D. linear is var. disholoma and so on in ore-field will fade green and become yellow. When the palnts are seriously poisoned, a lot of yellow-brown spots appear on their leaves. The conifor of conferous tree Pinus massoniana turn red or red brown most of leaves become withered and some brand died. These ecology change result in existing the so called polychrome plant community in this area, i.e. leaves of plants have become green, yellow, brown, red and grey. Table 1 Mo contents in rock, soil and plants
(ppm). Note : 02 pinus massoniana
03-Rhodomyrtus tomentosa 04-Itea Chinesis 05-D-var dchotoma.
When Mo content is 5-50 ppm in soil, Mo can help plants grow. The appearance of plant community trends to normal. The growing and development of the leguminous plant is good with green and large and normal flower and fluid. But if Mo is less than 5 ppm in soil, the leguminous plant growing is unhealthy owing to lack of nutritions. Excess Mo content is soil will bring about excess Mo existences in plant. As a result, it effects on the absorption and conveyance of Mg, Mo, Fe, Cu and Zn in plant, resulting inlosing the Fe/Mo, Mg/Mo, Cu/Mo, Zn/Mo and Mn/Mo balance in plants, especially the Mg content obviously reduced, which effects on chlorophyll metabolism and pholosynthesis. The following phenomena took place: chlorophyll content is reduced and the blade calls are destroyed, green leaves turn into yellow, appearing brown-yellows spots, leaf peak withered and become yellow. These plant physiology and ecology change caused by excess Mo leads to the change of the reflective spectrum characteristics of the plants. Spectrum and image characteristics of poisoned plants. In visible and near infrared wave band, the reflectivity of poisoned plant is generally higher than that of the normal plant. It is by about 2-4% in blue band, 3-4% in green light band, 2% in red light band and 10-15% in near infrared band. But it is contrary in infrared wave band. The more the poisoned degree of the plants is the larger the difference of their reflectivity is, in comparison to that of plants in normal area. There are some differences in plant reflectivity in Nov. and Jan. which is higher than that in May. In addition, the reflectivity difference between the poisoned and normal plants is obvious in Nov. and Jan. By means of differential and Cheboshed plynome analyse of spectrum data, the authors found that blue shift commonly exists in the spectrum of the poisoned plants. It is about 40-80A (maximum 180A). after green regrettable indexes (TM4/TM3) analyze, the index of plants in Mo ore field or alteration zone is lower that n that in normal area, showing that the plant luxuriant degree in ore-field is lower than that in normal area and content of chlorophyll is lower. During transmissivity measurement for the negative film of ground narrow band spectrum, it is best to measure the transmissivity of the film at its blank as a criterion to overcome the effect Caused by different film type, photographic speed and develop condition. The result shows a regular change. In Nov. their transmissivities are Mo ore-field < alteration zone < normal area. It lowers by about 1-30% in Mo-ore-field. The trnasmissivities of aerial multispectral negative in been carried out for the aerial multispectral image of the MSS red, green and blue bands. The composite film in Mo ore-field emerges a normal brown-drab and that in the normal area is yellow brown. The grey rang of the positive film in Dec., 1989 is Mo ore-field < alteration zone band, then, the KL change is performed for the composite is also done for the TM CCT 5,4 and 2/3 band, then the KL change is performed for the composite image. In Mo ore-field it appears brown-drab with half ring like, but that in normal area is yellow-brown. The relative analyses between the Mo contents in rock, soil and plants, plant blade pigment and moisture, the spectrum characteristics of plants and image feature (ground narrow band spectrum photo aerospace) indicates that there is a good relativity. It is know form these facts that grey range of TM is mainly restricted by Mo content in soil and blade; secondly by the blade pigment and moisture of the plants. In summary, the high Mo content in soil resulting from high Mo content in rock leads to plants being poisoned and making a change of chlorophyll content, structure, moisture of the blade. These ill effect on the plans spectrum reflectivity. The anormal reflection result in appearance of anormal color in the aerial multispectral flaes color composite image and Mo ore-field. Conclusions The authors have applicated the principle and method mentioned above to search for Au-deposit in Yexi, Haina region and 5 prospective and 2 target for Au have been found. The remarkable social and economical are achieved. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||