This paper reports preliminary results from an investigation of organic matter (OM) from the Carboniferous coarse to fine grained clastic sequences of the Salmon River Basin, Nova Scotia, Canada. The study focuses on the lead-zinc bearing fluviatile sandstone of the Yava ore deposite and its purpose is to explore how the metalliferous fluids might have modified the OM for different lithologies near the ore body. Previous researches have shown that vitrinite reflectance ( R o-vi) of OM in sandstone increases both with depth and regionally toward the Yava area. This lead previous investigators to conclude that the R o-vi was due to thermal effects of mineralizing fluids. On the other hand, thermal alteration index (TAI), based on spores from interbedded shales, is quite homogenous throughout the area and with values too low to fit with the maturation rank based on R o-vi. In the latter case the present authors argue that oxidizing effects of the metalliferous fluids are responsible for higher and increasing R o-vi in the more porous and permeable sandstone. Organic matter petrography, reflectance, fluorescence, color estimation, pyrolysis, ultimate analysis and scanning electron microscopy techniques were used to study 159 samples from 69 boreholes and hand specimens. OM petrography proved to be the most conclusive technique while reflectance and color evaluation support their results. The bulk of OM occurs as dispersed coaly fragments and thinly bedded coal in sandstone units. Rather undeformed and well preserved tree parts from sandstone and finer clastic rock show distinct morphology. Rare fractures filled with solid bitumen occur throughout the sequence. Macerals are mainly composed of vitrinite which exhibits increasing galena-sphalerite replacement toward the ore zone as showed by scanning electron microscopy microanalysis. Amongst secondary macerals, small trilete spores prevail. Alteration features such as rims, bireflectance or anisotropy, hydrogenation or etching of vegetal textures, dessication cracks and cavities are regionally developed in vitrinite, inertinite and solid bitumen. In the ore zone, degasification features are preferentially developed in textinite while decreasing R o-vi values, accompanied by anisotropy, are best seen in collinite. The increasing anisotropy toward sulfide accumulation exceed 50% for R o-vi values as low as 0.86%. These features, along with the fact that the lowest TAI values (2-) are observed toward the ore deposit, support the hypothesis of chemical alteration of OM rather than by thermal processes. Fluorescence of exinitic material is weakly preserved outside the ore deposit but dissappears where OM exhibits either sulfide filling of laminae, microfractures or dessication cracks. It is most obvious in sphalerite where OM exhibits either sulfide replacement or sulfide filling of laminae, microfractures or dessication cracks. The fluorescence is most marked in sphalerite from the mineralized samples. Increasing R o-vi values with depth is noted for half of the boreholes, amongst which several abnormally high reflectance gradients, up to 7% of R o-vi/km, have been measured. The other half of the boreholes shows decreasing values or no gradation with respect to their R o-vi. Although a slight trend of increasing R o-vi values is noted towards the Yava deposit, this cannot be generalized to the entire area. Results from the ultimate analysis (H/C, O/C) support the type and rank of OM as estimated under the microscope. To date, pyrolysis technique (Rock-Eval) appears to be less conclusive. A lot of results on the Van Krevelen diagram suggests an impoverishment of oxygen content in OM. Lack of oxygen effects on pyrolysis supports this suggestion. This research in progress points to the possible reticulation of OM causing “retrograde reflectance” and possibly will allow discrimination between thermal and chemical alteration of organic matter in the proximity of ore fluids. Although well established parameters do not support totally the chemical character of the alteration in the Yava region, the discrepancy between TAI and R o-vi values and the absence of mosaic texture in high R o-vi gradient sequences preclude a solely thermal process to account for the evolution of the optical properties of the OM.