The NE-Hungarian Darnó Unit hosts both Triassic and Jurassic pillow basalt blocks in an accretionary mélange. This Unit can be correlated with similar mélange complexes in the Dinarides and Hellenides. The studied epigenetic veins of the Darnó Unit are found in both Triassic and Jurassic basalts, however similar veins were recognized in the Triassic basalt of the Croatian Medvednica Mts. and in the Greek Stragopetra Mts., too. All studied veins contain mostly quartz and prehnite with a small amount of Cu- and Fe-bearing ore minerals. At the vein-basalt contact, clasts of the host rock and pumpellyite, chlorite, epidote are found. The primary ore minerals are chalcopyrite and bornite, but their alteration products also occur. Based on the fluid inclusion study of the quartz, the minimum formation temperature is between 169-228°C at the Darnó Hill, 110-212°C at the Medvednica Mts. and 183-259°C at the Stragopetra Mts. The salinity of the parent fluid was 2-3 NaCl equiv. wt% at both localities. Quantitative analysis of chlorite associated with the quartz allows calculating 228-258°C (Darnó Hill) and 212-216°C (Medvednica Mts.) as formation temperatures. Joint results of the above mentioned two methods define a pressure range of 10-110 MPa (Darnó Hill) and 55-245 MPa (Medvednica Mts.) for the vein formation. The observed characteristics suggest similar formation process in similar environment for both localities. The found p, T and salinity conditions, as well as the trace element composition of the ore minerals rule out the submarine hydrothermal process origin. The observed characteristics and the fact, that the veins are located in different aged basalts suggest an epigenetic process related origin. Based on earlier studies, an Alpine regional metamorphic process affected on the region and according to the results of the present research, the veins could form in the prograde or the retrograde phase of this metamorphism.