The following plot shows the price of gold in both nominal and inflation adjusted (2016) dollars vs. the federal funds rate. The correlation is not strong. I’m not a statistician, and hence am not certain regarding the applicability of Kendall rank correlation coefficient and Spearman rank correlation coefficient to this data. But for what its worth the Kendall correlation between Fed fund rate and nominal gold price is -0.119. The Spearman correlation is -0.213. The negative value means that as one variable increases (interest rate), the other variable (nominal gold price) decreases. The possible range is -1 to 1. The slight negative values indicating a weak negative correlation, which is not inconsistent with the figure below. However, if you look at the data over the time period about 1975-1985, and then again over the time period around 2005-2015, you see quite different behavior. Based on this data, it doesn’t look to me like the Fed fund rate is a good predictor of the direction that gold prices will take.
GOLD PRICE VS FED FUND RATE