How to plot the means using ggtern

I would like to plot the means of a dataset on a ggtern plot.

I found triangle.plot from ade4 library but I would like to do the same using ggtern (it will be easier to modify all the settings). I saw geom_crosshair_tern() but was not able to adapt it.

library(ade4)
data(euro123)
tot <- rbind.data.frame(euro123$in78, euro123$in86, euro123$in97)
row.names(tot) <- paste(row.names(euro123$in78), rep(c(1, 2, 3), rep(12, 3)), sep = "")
triangle.plot(tot, addmean=TRUE,show.position = FALSE)

Here is something to get you started:

library(ggtern)
library(plyr)
df.tot = tot
df.mu = as.data.frame(t(colMeans(tot)))
ggtern(data=df.tot,aes(pri,ter,sec)) + 
  geom_point() +
  geom_crosshair_tern(data=df.mu) +
  geom_point(data=df.mu,color='red') + 
  geom_label(data=100*df.mu,
             aes(
               y = ter - 5,
               label=sprintf("P=%.1f, S=%.1f, T=%.1f",pri,sec,ter)
             ),
             size=3,
             color='red'
             ) + 
  theme_bw() +
  theme_showarrows() + 
  limit_tern(0.8,0.5,0.7) +
  labs(
    x = 'Pri',xarrow='Primary',
    y = 'Ter',yarrow='Tertiary',
    z = 'Sec',zarrow='Secondary'
  )