I think Thermal Expansion is the mod which generates Copper, Tin, Lead, Silver and Nickle in Tekkit. The ore generation settings appear to be this:
I:Ore.Copper.ClusterSize=8
I:Ore.Copper.MaxY=75
I:Ore.Copper.MinY=40
I:Ore.Copper.NumClusters=10
I:Ore.Lead.ClusterSize=8
I:Ore.Lead.MaxY=35
I:Ore.Lead.MinY=10
I:Ore.Lead.NumClusters=4
I:Ore.Nickel.ClusterSize=4
I:Ore.Nickel.MaxY=20
I:Ore.Nickel.MinY=5
I:Ore.Nickel.NumClusters=2
I:Ore.Silver.ClusterSize=8
I:Ore.Silver.MaxY=30
I:Ore.Silver.MinY=5
I:Ore.Silver.NumClusters=3
I:Ore.Tin.ClusterSize=8
I:Ore.Tin.MaxY=55
I:Ore.Tin.MinY=20
I:Ore.Tin.NumClusters=7
You'll only want the MinY and MaxY parts, but the rest is good to know anyway