The molecular and petrographic characteristics of organic matter in internal sediments from the Mississippi Valley-type lead-zinc deposits in southern Poland reveal immature and well-preserved organic matter. Huminite reflectance values of organic matter in all internal sediments are low, with a mean value of 0.29%, corresponding to a lignite range of coalification. Most organic compounds in the organic matter (e.g., cadalene, retene, simonellite, perylene, and β-sitosterol and its transformation products stigmastanol and stigmasta-3,5-dien-one), as well as lignin degradation compound products (e.g., benzoic acid, vanillin, 4-benzaldehyde, benzenedicarboxilic acids, and hydroxybenzoic acids), are of terrestrial origin. Monosaccharides with dominant α- and β-glucose were identified as possible remnants of cellulose degradation products, suggesting an excellent state of organic matter preservation, given that monosaccharides are preserved only under conditions of limited oxygen after sedimentation, resulting from the rapid accumulation of internal sediments in meteoric paleokarst cavities followed by insignificant diagenesis. Petrologic and palynological data on internal sediments clearly indicate a Middle Triassic age for organic matter and for the development of a Triassic meteoric karst system immediately after Anisian carbonate sedimentation.