[en] This report describes the lithology and geological structures of the ONKALO underground rock characterization facility access tunnel in chainage 990-1980. This part of the tunnel was excavated and mapped from spring 2006 to spring 2007. The bedrock is very heterogenic and mainly composed of veined gneiss and diatexitic gneiss but many dykes and sections of pegmatitic granite also occur. In addition, small sections of stromatic gneiss and K-feldspar porphyry are present. There are also numerous inclusions of mica gneiss, quartz gneiss and skarn. The foliation dips moderately towards SE. 22 fold axes and 22 axial planes were measured from the ONKALO tunnel in chainage 990-1980 and all except one have been interpreted to belong to deformation phase D3. The measured fold axes have various orientations, but most have moderate plunges and ENE or WSW-trending ones dominate. The axial planes typically plunge moderately towards SE. A total of 10355 fractures were measured. Three main fracture sets were distinguished from the measured orientations: set 1 fractures are more or less horizontal, set 2 fractures are vertical and trend approximately ENE-WSW. The set 3 fractures are vertical and NWN-SES trending. Among the longer fractures (1 m and over in length) also a fourth set was observed. The set 4 fractures are, parallel to the foliation, NE-SW trending and moderately dipping. From the measured fractures, 395 were slickensided. The slickensided fractures are mainly either vertical N-S trending (set 3) or parallel to the foliation, trending NE-SW with moderate dip to SE. Measurements from slickenside surfaces show lineations plunging mainly to N or E with shallow dip. Sense of movement for the slickenside surfaces varies. The chainage 990-1980 contains 127 tunnel-crosscutting fractures with mostly vertical, N-S trending (set 3) or subhorizontal (set 1) orientation. The most common filling minerals are calcite, pyrite, chlorite, kaolinite, chlorite, epidote and muscovite. Also 21 deformation zone intersections were observed, 17 brittle deformation intersections and 4 high-grade ductile zones. Q-classification was used in order to determine the rock mass quality in the tunnel, and it was determined separately for every ∼ 5 m long section. The Q-quality varies from poor to exceptionally good, being mainly extremely good. The low quality (poor) is restricted to a 1m wide area at chainage 1823 where the tunnel is cut by the ONK-100 fault zone. (orig.)