Horizon of Progress's first ability checks the effects of all mana-producing abilities of lands you control, but it doesn't check their costs or legality. For example, Spire of Industry says ", Pay 1 life: Add one mana of any color. Activate only if you control an artifact." If you control Spire of Industry and Horizon of Progress, Horizon of Progress's first ability can generate any color of mana. It doesn't matter whether you control an artifact or whether Spire of Industry is untapped.