The state of Rajasthan is endowed with world class base metal deposits notably the Pb-Zn deposits of Zawar, RajpuraDariba and Rampura-Agucha and copper in Khetri- Nim ka Thana belt. The present note reports the geological attributes of a major new find of unusually thick copper mineralisation in Alwar basin of North Delhi Fold Belt (NDFB) that holds potential for a large copper deposit of economic significance. The mineralization is restricted to the Ajabgarh Group which comprises of argillaceous, arenaceous and calcareous components (Banerjee, 1980; Mukhopadhyay, 2009). The Kushalgarh, Seriska, Thanaghazi, Bharkol and Arauli Formations from bottom to top constitute the Ajabgarh Group. Kushalgarh Formation overlies the quartzite of the Pratapgarh Formation with a sharp contact and is represented by biotite-marble, banded calcareous semi-pelite and quartzite. The present work is restricted to the Thanagazhi Formation of the Ajabgarh Group (Boopathi, 2010). Thanaghazi Formation has a gradational contact with the overlying Bharkol Formation (Singh, 1988). The lower part is calcareous and is associated with quartzite. At several places spotted and pyritiferous phyllites overlie the carbon phyllite.The Alwar basin in the NDFB is known for several incidences of copper and two small copper deposits were reported by GSI at Bhagoni and Kho-Dariba. Copper dominated geochemical anomalies have been reported from the Alwar basin at a number of places, but thick mineralisation of economic significance remained elusive to the mappers and exploration geologists. Reconnaissance prospecting that was followed by detailed mineral exploration by the present authors has led to the first time discovery of an unusual very thick copper mineralisation in Mundiyawas-Khera area in Alwar basin. The explored block (Latitude 27o21'00" to 27o23' 00" N, Longitude 76o16' 30" to 76°17'35" E) is located 5 km SSW of Tehsil headquarter Thanaghazi, Alwar district, Rajasthan.