Not directly lithium, but all pathfinders and K/rb ratios all...

Not directly lithium, but all pathfinders and K/rb ratios all which can give a pretty good indication of a fertile granite.

Certainly will tell you if its not fertile. one manufacturer state the below:

"

• Identify and assess granitic parent rock fertility with respect to the hosting potential of LCT pegmatites. Fertile granites exhibit elevated Rb, Cs, Sn, and Ta, as well as lower K/Rb ratios than typical granites.
• Differentiate rare metal-bearing pegmatites from barren, more typical pegmatites with granitic composition and to differentiate LCT-pegmatites from NYF-pegmatites.
• Act as a proxy for lithium grade, where a strong correlation exists with pathfinder elements (Rb in particular) and has been determined by a detailed orientation survey with sufficient quality laboratory data (shown in Figure 2).
• Directly analyze outcrop, surface soil samples, and drilling cuttings. In particular, Sn, Sb, and As, can be used effectively to map out surface anomalies where Li, Cs, K, and Rb have been mobilized and/or depleted.
• Analyze whole rock chemistry (Mg, Al, Si, K, Ca, and Fe) and immobile trace elements (such as Ti and Zr) for litho-geochemistry to determine deposit stratigraphy, alteration, and pegmatite zonation. "