Deposit Image Model and optimization of Prospect Targets
B. Intermediate-basic volcanic rock type deposit image model
- Intermediate-basic volcanic formation are controlled by faults, displaying zonal distribution of east-west orentation and dark, dark-blue colour composite image (fig.3) . Accordingly three intermediate-basic volcanic zones interpreted and their distribution has been delineated.
Figure 3 Colour composite image
- Deposits are emplaced at the intersections of NE and NW faults which can be easily regnized in the image.
- Light-coloured alteration related to mineralization displays grey, light grey, light green
colour in the colour composite image (4,5,7) . in contrast with dark-blue background colour caused by intermediate-basic volcanic rocks the light-coloured alternations are distinguished and their spatial distribution is easily delineated.
- Late small intrusive bodies which are closely relevant with gold mineralization in space and time show light purple colour in the colour composite image (4,5,7 bands) . In addition circular structures which reflect center of volcanic activities are important image signatures for this the type deposits.
C. Metamorphic rock-type deposit image model
Metamorphic rock-type deposits in the study region are referred to those which occured in ordovician-Silurian systems and Lower Proterozoic slightly metamophic rocks.
(A) Lower proterozoic comprises, in ascending order, magmatite, marble and inthe upper part metamorphic rock formation characterized by occurrence of bi-modal volcanic rocks. In KL transform image, migmatite and different degrees of magmatization are well displayed. Bimodal volcanic rocks display dark, dark brown colour on both 2,7,5 and 4,5,7 band colour composite image . So regional distribution of the third subgroup of Lower Proterozioc ( target horizon for occurrence of gold deposists) is distinctly demonstrated. In some areas, these target horizons are controlled by east-west folding, showing symmetrically zonal distribution along the north and south limbs of folding.
(B) In some areas, combination charcteristics of image signatures which reflected different lithological assemblage are vary distinct. ore-bearing strata (basic and intermediate colcanic rocks) display dark brown colour, while granite and quartz diorate light grey colour, syeniteporphyry dark-red brown colour, showing alternating banded signatures in the colour composit image (2,7,5 bands).
(C) Light-coloured alternation displays grey, light blue colour in the colour composite image (1,7,5 bands ), exhibiting narrow bands and linear distribution. These image features are remarkably distinct from the dark brown colour background caused by ore-bearing formations.
4. Target Optimization
The final purpose of study or regional gelogy, metallogenic regularities and image features is to optimize targets. Based on the analyses of regional geological evolution, gold mineralization distribution regularities, prognosis criteria of gold deposits have been determined . Exploring the inherent links between prognosis criteria and image features and converting ore-controlling factors (Includeing structures, intrusive bodies, gold-source formations, alternations) into recognizable eleven favourable areas have been predicted.
Taking J-1 for example . According to established image model, except favourable structures and gold source conditions which should be considered, image feature of ore-bearing granite bodies are also important cirterion in predicting potential area. first, colour composite method is used to sieve favorable granite bodies having image features similar to known mineralized granic bodies.
Redults of Applicaton
After selecting favourable areas, field check has been done. Preliminary investigation has indicated that geochemical anomalies and gold mineralization have been found in three of the predicted areas . The results are satisfactory.
Implications
Remote sensing practice in Beishan region has shown that applying deposite image model to mineral prognosis is an effective, fast tool for regional assessment. it has a lot of advantages over conventional geological methods. It is suitable for regional recconaissance, especially for remote areas with poor transformation condition and basic geological information . The methods is of certain universal significance in theory and practice.
Reference
- Cui zhekui and others, 1988, Application results of TM Image in Beishan Region, Radiogeology Newsletter , 1988-7
- J.J. bache , 1987 , world Gold Deposits: A Geological Classification
- Floyd F. Sabins , JR. 1987 , Remote Sensing Principles and interpreation
- Beijing Research Institute of Uranium Geology, Computer Application Institute of Nuclear Industry, 1988, Synopsis pof TM Data processing and Application in Gold Recconaissance Uranium and Gold newsletter, 1988-15 .
