The symptoms on this geranium are due to iron and manganese toxicity, a nutritional disorder associated with low growing medium pH (below 6.0). This problem is sometimes called "bronze speckle" due to the numerous small brown spots on the leaves. Zonal geranium, American marigold and all types of impatiens are susceptible.
See the fact sheets: pH and Fertility Review for Annuals, University of Massachusetts
Iron Out, University of Florida Extension