Assuming that you know how compile a .Rnw file with knitr
and biblatex, just compliging this file all the references of non-base attached packages in the R session are stored automatically in a .bib file and then you can use as usual with BibTex, or as in this example, with biblatex and biber
:

\documentclass{beamer}
\usepackage{biblatex}
\addbibresource{test.bib}
\begin{document}
<<echo=F,message=F>>=
# R packages loaded only to test their references
library(xtable)
library(stargazer)
library(ggplot2)
library(pscl)
write_bib(names(sessionInfo()$otherPkgs),file="test.bib")
@
\begin{frame}[t,allowframebreaks]{References}
\nocite{*}
\printbibliography
\end{frame}
\end{document}